diff --git a/satpy/readers/avhrr_l1b_gaclac.py b/satpy/readers/avhrr_l1b_gaclac.py
index 47f0d97283..34945ddb80 100644
--- a/satpy/readers/avhrr_l1b_gaclac.py
+++ b/satpy/readers/avhrr_l1b_gaclac.py
@@ -43,7 +43,7 @@
 from pygac.lac_pod import LACPODReader
 
 from satpy.readers.file_handlers import BaseFileHandler
-from satpy.utils import get_legacy_chunk_size
+from satpy.utils import datetime64_to_pydatetime, get_legacy_chunk_size
 
 logger = logging.getLogger(__name__)
 
@@ -185,8 +185,8 @@ def get_dataset(self, key, info):
 
         # Update start/end time using the actual scanline timestamps
         times = self.reader.get_times()
-        self._start_time = times[0].astype(dt.datetime)
-        self._end_time = times[-1].astype(dt.datetime)
+        self._start_time = datetime64_to_pydatetime(times[0])
+        self._end_time = datetime64_to_pydatetime(times[-1])
 
         # Select user-defined scanlines and/or strip invalid coordinates
         if (self.start_line is not None or self.end_line is not None
@@ -224,8 +224,8 @@ def slice(self, data, times):  # noqa: A003
         """
         sliced = self._slice(data)
         times = self._slice(times)
-        self._start_time = times[0].astype(dt.datetime)
-        self._end_time = times[-1].astype(dt.datetime)
+        self._start_time = datetime64_to_pydatetime(times[0])
+        self._end_time = datetime64_to_pydatetime(times[-1])
         return sliced, times
 
     def _slice(self, data):
diff --git a/satpy/readers/gms/gms5_vissr_l1b.py b/satpy/readers/gms/gms5_vissr_l1b.py
index 51f33d657a..7fb75c062b 100644
--- a/satpy/readers/gms/gms5_vissr_l1b.py
+++ b/satpy/readers/gms/gms5_vissr_l1b.py
@@ -164,7 +164,7 @@
 from satpy.readers.file_handlers import BaseFileHandler
 from satpy.readers.hrit_jma import mjd2datetime64
 from satpy.readers.utils import generic_open
-from satpy.utils import get_legacy_chunk_size
+from satpy.utils import datetime64_to_pydatetime, get_legacy_chunk_size
 
 CHUNK_SIZE = get_legacy_chunk_size()
 
@@ -307,8 +307,7 @@ def _get_orbital_parameters(self):
         }
 
     def _get_time_parameters(self):
-        start_time = mjd2datetime64(self._mode_block["observation_time_mjd"]).astype("datetime64[us]")
-        start_time = start_time.astype(dt.datetime).replace(second=0, microsecond=0)
+        start_time = self._get_start_time()
         end_time = start_time + dt.timedelta(
             minutes=25
         )  # Source: GMS User Guide, section 3.3.1
@@ -317,6 +316,11 @@ def _get_time_parameters(self):
             "nominal_end_time": end_time,
         }
 
+    def _get_start_time(self):
+        start_time = mjd2datetime64(self._mode_block["observation_time_mjd"])
+        start_time = datetime64_to_pydatetime(start_time)
+        return start_time.replace(second=0, microsecond=0)
+
     def get_dataset(self, dataset_id, ds_info):
         """Get dataset from file."""
         image_data = self._get_image_data()
diff --git a/satpy/readers/viirs_vgac_l1c_nc.py b/satpy/readers/viirs_vgac_l1c_nc.py
index 2f43ffd2a2..116bd0e5c9 100644
--- a/satpy/readers/viirs_vgac_l1c_nc.py
+++ b/satpy/readers/viirs_vgac_l1c_nc.py
@@ -22,7 +22,7 @@
 import xarray as xr
 
 from satpy.readers.file_handlers import BaseFileHandler
-from satpy.utils import get_legacy_chunk_size
+from satpy.utils import datetime64_to_pydatetime, get_legacy_chunk_size
 
 CHUNK_SIZE = get_legacy_chunk_size()
 logger = logging.getLogger(__name__)
@@ -75,9 +75,7 @@ def set_time_attrs(self, data):
 
     def dt64_to_datetime(self, dt64):
         """Conversion of numpy.datetime64 to datetime objects."""
-        if isinstance(dt64, np.datetime64):
-            return dt64.astype(dt.datetime)
-        return dt64
+        return datetime64_to_pydatetime(dt64)
 
     def extract_time_data(self, data, nc):
         """Decode time data."""