[asgfoi]

The problem they are addressing is already solved. Simply say at time X Y, where X is the time and Y is the offset, preferably an established offset.

We meet at 12:00 GMT

Done

Everyone only needs to remember one number, their local offset to GMT. If someone uses an, to the receiver, unknown offset, then look it up and do some first grade math.

[Moru]

This is very hard when you first have to explain what timezones are for some people (no countries mentioned...). When I was playing MMORPGS most, 10 years ago this was the main problem to set a time for a quest.