text: Title: fix `IsNow`
  Body: The following should pass
  
  ```py
  assert '2022-07-15T10:56:38.311Z' == IsNow(delta=10, tz='utc', format_string='%Y-%m-%dT%H:%M:%S.%fZ', enforce_tz=False)
  ```
  
  (ignoring that that's not "now" any longer obvisouly)