diff --git a/tests/api/test_search.py b/tests/api/test_search.py
index d3d4177..15fd19c 100644
--- a/tests/api/test_search.py
+++ b/tests/api/test_search.py
@@ -1,4 +1,3 @@
-import time
 from datetime import datetime, timedelta, timezone
 
 import pytest
@@ -56,7 +55,7 @@ def test_invalid_spatial_search():
 
 def test_temporal_search_single_tailed():
     # Test single tailed
-    utcnow = datetime.now(timezone.utc).replace(microsecond=0, tzinfo=timezone.utc)
+    utcnow = datetime.now(timezone.utc)
     utcnow_str = utcnow.isoformat()
     search = Search(collections=["collection1"], datetime=utcnow_str)
     assert search.start_date is None
@@ -65,7 +64,7 @@ def test_temporal_search_single_tailed():
 
 def test_temporal_search_two_tailed():
     # Test two tailed
-    utcnow = datetime.now(timezone.utc).replace(microsecond=0, tzinfo=timezone.utc)
+    utcnow = datetime.now(timezone.utc)
     utcnow_str = utcnow.isoformat()
     search = Search(collections=["collection1"], datetime=f"{utcnow_str}/{utcnow_str}")
     assert search.start_date == search.end_date == utcnow
@@ -108,12 +107,11 @@ def test_invalid_temporal_search_too_many():
 def test_invalid_temporal_search_date_wrong_order():
     # End date is before start date
     start = datetime.now(timezone.utc)
-    time.sleep(2)
-    end = datetime.now(timezone.utc)
+    end = start - timedelta(seconds=100)
     with pytest.raises(ValidationError):
         Search(
             collections=["collection1"],
-            datetime=f"{end.isoformat()}/{start.isoformat()}",
+            datetime=f"{start.isoformat()}/{end.isoformat()}",
         )
 
 
diff --git a/tests/test_models.py b/tests/test_models.py
index 0a9a22f..b811e96 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -166,6 +166,37 @@ def test_api_context_extension() -> None:
     ContextExtension(**context)
 
 
+@pytest.mark.parametrize(
+    "args",
+    [
+        {"datetime": "2024-01-01T00:00:00Z"},
+        {
+            "datetime": None,
+            "start_datetime": "2024-01-01T00:00:00Z",
+            "end_datetime": "2024-01-02T00:00:00Z",
+        },
+    ],
+)
+def test_item_properties_dates(args) -> None:
+    ItemProperties(**args)
+
+
+@pytest.mark.parametrize(
+    "args",
+    [
+        {"datetime": None},
+        {"datetime": None, "start_datetime": "2024-01-01T00:00:00Z"},
+        {"datetime": None, "end_datetime": "2024-01-01T00:00:00Z"},
+    ],
+)
+def test_item_properties_no_dates(args) -> None:
+    with pytest.raises(
+        ValueError,
+        match="start_datetime and end_datetime must be specified when datetime is null",
+    ):
+        ItemProperties(**args)
+
+
 def test_declared_model() -> None:
     class TestProperties(ItemProperties):
         foo: str