[bloak]

> I feel the standard interchange format for datetimes really should be 64 bit Unix timestamps.

Several people have already replied pointing out that for scheduling events in the future, particularly recurring events, it's practically necessary to refer to time zones.

So I'll just mention the problem of leap seconds, which are announced six months in advance. If a one-second error could cause problems then probably you should use TAI rather than UTC. But you still need UTC for other purposes, so probably you need both and so you need to keep track of whether a particular timestamp is TAI or UTC.