diff --git a/src/toast/intervals.py b/src/toast/intervals.py
index 0f199193b..b475e2585 100644
--- a/src/toast/intervals.py
+++ b/src/toast/intervals.py
@@ -94,8 +94,16 @@ def __init__(self, timestamps, intervals=None, timespans=None, samplespans=None)
                     if np.isclose(timespans[i][1], timespans[i + 1][0], rtol=1e-12):
                         # Force nearly equal timestamps to match
                         timespans[i][1] = timespans[i + 1][0]
+                    # Check that the intervals are sorted and disjoint
                     if timespans[i][1] > timespans[i + 1][0]:
-                        raise RuntimeError("Timespans must be sorted and disjoint")
+                        t1 = timespans[i][1]
+                        t2 = timespans[i + 1][0]
+                        dt = t1 - t2
+                        ts = np.median(np.diff(timestamps))
+                        msg = f"Timespans must be sorted and disjoint"
+                        msg += f" but {t1} - {t2} = {dt} s = {dt / ts} samples)"
+                        raise RuntimeError(msg)
+                #  Map interval times into sample indices
                 indices, times = self._find_indices(timespans)
                 self.data = np.array(
                     [
@@ -186,7 +194,12 @@ def __len__(self):
         return len(self.data)
 
     def __repr__(self):
-        return self.data.__repr__()
+        s = "<IntervalList [\n"
+        for ival in self.data:
+            s += f" {ival.start:15.3f} - {ival.stop:15.3f} ({ival.first:9} - {ival.last:9}),\n"
+        s += "]>"
+        # return self.data.__repr__()
+        return s
 
     def __eq__(self, other):
         if len(self.data) != len(other):
diff --git a/src/toast/observation_dist.py b/src/toast/observation_dist.py
index af9d06c34..540765340 100644
--- a/src/toast/observation_dist.py
+++ b/src/toast/observation_dist.py
@@ -419,17 +419,14 @@ def global_interval_times(dist, intervals_manager, name, join=False):
         (list):  List of tuples on the root process, and None on other processes.
 
     """
-    ilist = [(x.start, x.stop, x.first, x.last) for x in intervals_manager[name]]
-    pstart = intervals_manager[name].timestamps[0]
+    ilist = [(x.start, x.stop) for x in intervals_manager[name]]
     all_ilist = None
     if dist.comm_row is None:
-        all_ilist = [(ilist, dist.samps[dist.comm.group_rank].n_elem, pstart)]
+        all_ilist = [ilist]
     else:
         # Gather across the process row
         if dist.comm_col_rank == 0:
-            all_ilist = dist.comm_row.gather(
-                (ilist, dist.samps[dist.comm.group_rank].n_elem, pstart), root=0
-            )
+            all_ilist = dist.comm_row.gather(ilist, root=0)
     del ilist
 
     glist = None
@@ -438,51 +435,22 @@ def global_interval_times(dist, intervals_manager, name, join=False):
         # the rank zero process of the observation is also the process with rank
         # zero along both the rows and columns.
         glist = list()
-
-        prev = None
-        cur = None
-        last_pn = None
-        global_off = 0
-        for pdata, pn, pstrt in all_ilist:
+        last_start = 0
+        last_stop = 0
+        for pdata in all_ilist:
             if len(pdata) == 0:
                 continue
-            for start, stop, first, last in pdata:
-                cur = [
-                    float(start),
-                    float(stop),
-                    int(global_off + first),
-                    int(global_off + last),
-                ]
-                if prev is None:
-                    # First global interval
-                    prev = cur
+            for start, stop in pdata:
+                # Avoid adding the same time span twice
+                if (
+                        np.isclose(start, last_start, rtol=1e-12) and
+                        np.isclose(stop, last_stop, rtol=1e-12)
+                ):
                     continue
-                if last_pn is not None:
-                    # We are on a later process's data, see if we had any continuation
-                    # of interval from last process.
-                    if prev[3] == global_off:
-                        # The previous interval ended at the final sample on that
-                        # process.  This means that the timestamp of the final sample
-                        # was artificially truncated.
-                        if cur[2] == 0 and join:
-                            # The first interval on this process starts at sample zero,
-                            # and we are joining intervals across the process boundary.
-                            prev[1] = cur[1]
-                            prev[3] = cur[3]
-                            continue
-                        else:
-                            # We are keeping any break between processes, but use
-                            # the first start time on this process as the stop time of
-                            # the interval from the previous process.
-                            prev[1] = pstrt
-                glist.append((prev[0], prev[1]))
-                prev = cur
-            last_pn = pn
-            global_off += pn
-
-        # Add final interval
-        if prev is not None:
-            glist.append((prev[0], prev[1]))
+                glist.append((start, stop))
+                last_start = start
+                last_stop = stop
+
     return glist
 
 
diff --git a/src/toast/ops/hwpss_model.py b/src/toast/ops/hwpss_model.py
index 1bcbfa3c8..992001e02 100644
--- a/src/toast/ops/hwpss_model.py
+++ b/src/toast/ops/hwpss_model.py
@@ -690,8 +690,11 @@ def _cut_outliers(self, obs, det_mag):
             all_dets = dets
             all_mag = mag
         else:
-            all_dets = flatten(obs.comm_col.gather(dets, root=0))
-            all_mag = np.array(flatten(obs.comm_col.gather(mag, root=0)))
+            all_dets = obs.comm_col.gather(dets, root=0)
+            all_mag = obs.comm_col.gather(mag, root=0)
+            if obs.comm_col.rank == 0:
+                all_dets = list(flatten(all_dets))
+                all_mag = np.array(list(flatten(all_mag)))
 
         # One process does the trivial calculation
         all_flags = None
diff --git a/src/toast/ops/pixels_wcs.py b/src/toast/ops/pixels_wcs.py
index 1a505fe3f..b225a7314 100644
--- a/src/toast/ops/pixels_wcs.py
+++ b/src/toast/ops/pixels_wcs.py
@@ -23,6 +23,18 @@
 from .operator import Operator
 
 
+def unwrap_together(x, y, period=2 * np.pi * u.rad):
+    """Unwrap x but apply the same branch corrections to y"""
+    for i in range(1, len(x)):
+        while np.abs(x[i] - x[i - 1]) > np.abs(x[i] + period - x[i - 1]):
+            x[i] += period
+            y[i] += period
+        while np.abs(x[i] - x[i - 1]) > np.abs(x[i] - period - x[i - 1]):
+            x[i] -= period
+            y[i] -= period
+    return
+
+
 @trait_docs
 class PixelsWCS(Operator):
     """Operator which generates detector pixel indices defined on a flat projection.
@@ -439,26 +451,29 @@ def _exec(self, data, detectors=None, **kwargs):
                 )
             minmax = minmax.T
             # Compact observations on both sides of the zero meridian
-            # can confuse this calculation. Use np.unwrap() to find
-            # the most compact longitude range.
-            lonmin = np.amin(np.unwrap(minmax[0]))
-            lonmax = np.amax(np.unwrap(minmax[1]))
-            if lonmax < lonmin:
-                lonmax += 2 * np.pi
+            # can confuse this calculation.  We must unwrap the per-observation
+            # limits for the most compact longitude range.
+            unwrap_together(minmax[0], minmax[1])
+            lonmin = np.amin(minmax[0])
+            lonmax = np.amin(minmax[1])
             latmin = np.amin(minmax[2])
             latmax = np.amax(minmax[3])
             if data.comm.comm_world is not None:
                 # Zero meridian concern applies across processes
-                all_lonmin = data.comm.comm_world.allgather(lonmin.to_value(u.radian))
-                all_lonmax = data.comm.comm_world.allgather(lonmax.to_value(u.radian))
-                all_latmin = data.comm.comm_world.allgather(latmin.to_value(u.radian))
-                all_latmax = data.comm.comm_world.allgather(latmax.to_value(u.radian))
-                lonmin = np.amin(np.unwrap(all_lonmin)) * u.radian
-                lonmax = np.amax(np.unwrap(all_lonmax)) * u.radian
-                if lonmax < lonmin:
-                    lonmax += 2 * np.pi
-                latmin = np.amin(all_latmin) * u.radian
-                latmax = np.amax(all_latmax) * u.radian
+                def gather(x):
+                    return (
+                        data.comm.comm_world.allgather(x.to_value(u.radian)) * u.radian
+                    )
+
+                all_lonmin = gather(lonmin)
+                all_lonmax = gather(lonmax)
+                all_latmin = gather(latmin)
+                all_latmax = gather(latmax)
+                unwrap_together(all_lonmin, all_lonmax)
+                lonmin = np.amin(all_lonmin)
+                lonmax = np.amin(all_lonmax)
+                latmin = np.amin(all_latmin)
+                latmax = np.amax(all_latmax)
             self.bounds = (
                 lonmin.to(u.degree),
                 lonmax.to(u.degree),
diff --git a/src/toast/spt3g/spt3g_export.py b/src/toast/spt3g/spt3g_export.py
index b24fdee9f..1ececb29b 100644
--- a/src/toast/spt3g/spt3g_export.py
+++ b/src/toast/spt3g/spt3g_export.py
@@ -10,7 +10,7 @@
 from astropy import units as u
 
 from ..instrument import GroundSite, SpaceSite
-from ..intervals import IntervalList
+from ..intervals import IntervalList, interval_dtype
 from ..timing import function_timer
 from ..utils import Environment, Logger, object_fullname
 from .spt3g_utils import (
@@ -167,7 +167,20 @@ def export_intervals(obs, name, iframe):
         (G3Object):  The best container available.
 
     """
-    overlap = iframe & obs.intervals[name]
+    overlap = []
+    frame = iframe.data[0]
+    for ival in obs.intervals[name]:
+        if frame.start <= ival.stop and frame.stop >= ival.start:
+            overlap.append((
+                ival.start,
+                ival.stop,
+                max(frame.first, ival.first),
+                min(frame.last, ival.last),
+            ))
+    overlap = IntervalList(
+        iframe.timestamps,
+        intervals=np.array(overlap, dtype=interval_dtype).view(np.recarray),
+    )
 
     out = None
     try:
diff --git a/src/toast/tests/helpers/ground.py b/src/toast/tests/helpers/ground.py
index 209029889..6e42e06ed 100644
--- a/src/toast/tests/helpers/ground.py
+++ b/src/toast/tests/helpers/ground.py
@@ -93,6 +93,7 @@ def create_ground_data(
     turnarounds_invalid=False,
     single_group=False,
     flagged_pixels=True,
+    schedule_hours=2,
 ):
     """Create a data object with a simple ground sim.
 
@@ -137,6 +138,7 @@ def create_ground_data(
         if tdir is None:
             tdir = tempfile.mkdtemp()
 
+        sch_hours = f"{int(schedule_hours):02d}"
         sch_file = os.path.join(tdir, "ground_schedule.txt")
         run_scheduler(
             opts=[
@@ -155,7 +157,7 @@ def create_ground_data(
                 "--start",
                 "2020-01-01 00:00:00",
                 "--stop",
-                "2020-01-01 06:00:00",
+                f"2020-01-01 {sch_hours}:00:00",
                 "--out",
                 sch_file,
             ]
@@ -218,6 +220,7 @@ def create_overdistributed_data(
     freqs=None,
     turnarounds_invalid=False,
     single_group=False,
+    schedule_hours=2,
 ):
     """Create a data object with more detectors than processes.
 
@@ -264,6 +267,7 @@ def create_overdistributed_data(
         if tdir is None:
             tdir = tempfile.mkdtemp()
 
+        sch_hours = f"{int(schedule_hours):02d}"
         sch_file = os.path.join(tdir, "ground_schedule.txt")
         run_scheduler(
             opts=[
@@ -282,7 +286,7 @@ def create_overdistributed_data(
                 "--start",
                 "2020-01-01 00:00:00",
                 "--stop",
-                "2020-01-01 06:00:00",
+                f"2020-01-01 {sch_hours}:00:00",
                 "--out",
                 sch_file,
             ]
diff --git a/src/toast/tests/ops_hwpss_model.py b/src/toast/tests/ops_hwpss_model.py
index f811fae88..5d6bc69c1 100644
--- a/src/toast/tests/ops_hwpss_model.py
+++ b/src/toast/tests/ops_hwpss_model.py
@@ -106,7 +106,7 @@ def create_test_data(self, testdir):
             weights,
             skyfile,
             "input_sky_dist",
-            map_key="input_sky",
+            map_key=map_key,
             fwhm=30.0 * u.arcmin,
             lmax=3 * pixels.nside,
             I_scale=0.001,
@@ -274,7 +274,7 @@ def test_hwpss_basic(self):
             os.makedirs(testdir)
 
         data, tod_rms, coeff = self.create_test_data(testdir)
-        n_harmonics = len(coeff) // 4
+        n_harmonics = len(coeff[data.obs[0].name]) // 4
 
         # Add random DC level
         for ob in data.obs:
@@ -331,7 +331,7 @@ def test_hwpss_relcal_fixed(self):
             os.makedirs(testdir)
 
         data, tod_rms, coeff = self.create_test_data(testdir)
-        n_harmonics = len(coeff) // 4
+        n_harmonics = len(coeff[data.obs[0].name]) // 4
 
         # Apply a random inverse relative calibration
         np.random.seed(123456)
@@ -400,7 +400,7 @@ def test_hwpss_relcal_continuous(self):
             os.makedirs(testdir)
 
         data, tod_rms, coeff = self.create_test_data(testdir)
-        n_harmonics = len(coeff) // 4
+        n_harmonics = len(coeff[data.obs[0].name]) // 4
 
         # Apply a random inverse relative calibration that is time-varying
         np.random.seed(123456)