IMHO this would to module 24 arithmetic, just like a normal clock.

When I do calculations with plain time that is what I want, if the date is also important I use datetime.datetime.  That a time value silently truncates when going past midnight is IMHO also the obvious behavior.

The biggest argument against adding this functionality I could come up with is that this can give wrong answers when daylight savings time transitions happen, which could lead to subtle bugs.