diff --git a/rattail_harvest/harvest/importing/model.py b/rattail_harvest/harvest/importing/model.py
index d445def..3a874c5 100644
--- a/rattail_harvest/harvest/importing/model.py
+++ b/rattail_harvest/harvest/importing/model.py
@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2022 Lance Edgar
+#  Copyright © 2010-2023 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -60,11 +60,15 @@ class TimeEntryImporter(ToHarvest):
         Fetch existing time entries from Harvest.
         """
         cache = {}
+
         # TODO: we try to avoid entries w/ timer still running here,
         # but for some reason they still come back, so double-check
-        entries = self.webapi.get_time_entries(**{'from': self.start_date,
-                                                  'to': self.end_date,
-                                                  'is_running': False})
+        kw = {'is_running': False}
+        if self.start_date:
+            kw['from'] = self.start_date
+        if self.end_date:
+            kw['to'] = self.end_date
+        entries = self.webapi.get_time_entries(**kw)
         for entry in entries:
             # double-check here
             if not entry['is_running']:
diff --git a/rattail_harvest/importing/harvest.py b/rattail_harvest/importing/harvest.py
index 348c24b..1e706a2 100644
--- a/rattail_harvest/importing/harvest.py
+++ b/rattail_harvest/importing/harvest.py
@@ -226,8 +226,12 @@ class HarvestTimeEntryImporter(FromHarvest, rattail_harvest_importing.model.Harv
     """
 
     def get_host_objects(self):
-        return self.webapi.get_time_entries(**{'from': self.start_date,
-                                               'to': self.end_date})
+        kw = {}
+        if self.start_date:
+            kw['from'] = self.start_date
+        if self.end_date:
+            kw['to'] = self.end_date
+        return self.webapi.get_time_entries(**kw)
 
     def normalize_host_object(self, entry):
         data = super(HarvestTimeEntryImporter, self).normalize_host_object(entry)
diff --git a/rattail_harvest/importing/rattail.py b/rattail_harvest/importing/rattail.py
index 54ce310..d61f3d8 100644
--- a/rattail_harvest/importing/rattail.py
+++ b/rattail_harvest/importing/rattail.py
@@ -61,6 +61,11 @@ class HarvestTaskImporter(base.FromRattail, rattail_harvest_importing.model.Harv
 class HarvestTimeEntryImporter(base.FromRattail, rattail_harvest_importing.model.HarvestTimeEntryImporter):
 
     def query(self):
-        query = super(HarvestTimeEntryImporter, self).query()
-        return query.filter(self.model_class.spent_date >= self.start_date)\
-                    .filter(self.model_class.spent_date <= self.end_date)
+        query = super().query()
+
+        if self.start_date:
+            query = query.filter(self.model_class.spent_date >= self.start_date)
+        if self.end_date:
+            query = query.filter(self.model_class.spent_date <= self.end_date)
+
+        return query