The best approach seems to be making a date+time either "timezone aware" or "naive" (I got this from python's datetime.) Naive dates don't have a timezone atta

The best approach seems to be making a date+time either "timezone aware" or "naive" (I got this from python's datetime.) Naive dates don't have a timezone attached, so of course there's no auto conversion. Aware times do. Now all you have to do is avoid assuming which your user wants. Especially avoid an interface that makes it look like they have a naive date when they actually have an aware one. For example, if the appointment is timezone-aware, then write the timezone next to it! So if the user writes 10:00 and you auto-convert that and print 10:00 EST, they at least have a chance to correct it.