diff --git a/sharded_queue/__init__.py b/sharded_queue/__init__.py
index 074405c..1303788 100644
--- a/sharded_queue/__init__.py
+++ b/sharded_queue/__init__.py
@@ -300,7 +300,7 @@ def calculate_timestamp(
         if isinstance(delta, str):
             return rrulestr(delta).after(datetime.now()).timestamp()
 
-        now: datetime = datetime.now()
+        now: datetime = datetime.now().replace(microsecond=0)
         if isinstance(delta, timedelta):
             now = now + delta