BUG: Fix dt64[non_nano] + offset rounding

Author: Aniketsy

pandas/core/arrays/datetimes.py

@@ -70,6 +70,7 @@
 
 from pandas.tseries.frequencies import get_period_alias
 from pandas.tseries.offsets import (
+ CustomBusinessDay,
  Day,
  Tick,
 )
@@ -824,8 +825,18 @@ def _add_offset(self, offset: BaseOffset) -> Self:
  "s",
  ]
  res_unit = self.unit
- if isinstance(offset, Tick):
- ns = abs(int(offset.value))
+ if isinstance(offset, Tick) or (
+ isinstance(offset, CustomBusinessDay)
+ and offset.offset is not None
+ and offset.offset.value != 0
+ ):
+ ns = abs(
+ int(
+ offset.value
+ if isinstance(offset, Tick)
+ else offset.offset.value
+ )
+ )
  if ns == 0:
  eff_unit = self.unit
  elif ns % 1_000_000_000 == 0: