Honestly I don't think timedelta cleanly maps to either of those concepts[1]. While it's true that when a timedelta is added to a datetime it behaves like a Period, when timedeltas are added or subtracted they behave more like Durations: adding several timedeltas just results in modding the number of seconds to be in [0, 86400) and assigning the rest to days (e.g. a timedelta of -1 seconds ends up being -1 days and +86399 seconds). So I don't think it can be extended to provide more human time operations.