BUG: Fix dt64[non_nano] + offset rounding

Author: Aniketsy

pandas/core/arrays/datetimes.py

@@ -824,9 +824,13 @@ def _add_offset(self, offset: BaseOffset) -> Self:
                 "s",
             ]
             res_unit = self.unit
-            if hasattr(offset, "offset"):
-                offset_td = Timedelta(offset.offset)
-                ns = abs(int(offset_td.value))  # Timedelta.value is in nanoseconds
+            offset_td = getattr(offset, "offset", None)
+            if (
+                offset_td is not None
+                and isinstance(offset_td, Timedelta)
+                and offset_td.value != 0
+            ):
+                ns = abs(int(offset_td.value))
                 if ns == 0:
                     eff_unit = self.unit
                 elif ns % 1_000_000_000 == 0:
@@ -837,7 +841,6 @@ def _add_offset(self, offset: BaseOffset) -> Self:
                     eff_unit = "us"
                 else:
                     eff_unit = "ns"
-
                 idx_self = units.index(self.unit)
                 idx_eff = units.index(eff_unit)
                 res_unit = units[min(idx_self, idx_eff)]