For most people, though, hours of availability can be more or less implicit. If I'm scheduling a phone call with a business person who works in an office, I can assume that their availability will probably be highest sometime around 10AM to 5PM in their local time zone. This is less true for hackers, and for self-employed people who don't spend a lot of time interacting with office workers, of course.
> For most people, though, hours of availability can be more or less implicit.
For most people I'm quite sure hours of availability can not be guessed based on what timezone they are in, most people are busy, their windows of availability are much more narrow than 8am-5pm, and surprisingly often they are available outside that range.
Even in those cases, the quantity of information you need stays constant. Now, you need their time zone. With UTC everywhere, you need their hours of availability.
There is currently some implicit transfer here, in that if they're in an office in Timbuktu, you can figure out their time zone without asking. But you should still coordinate with them, at which point you can find out their hours.... And I'm sure that in a world where everything is UTC, looking up a particular place's customary business hours will be no more difficult than it currently is to look up a particular place's time zone.
