I've thought about this a lot too...one-hour gradiant jumps also make little sense and are only "accurate" for some point roughly in the center of the zone. So

I've thought about this a lot too...one-hour gradiant jumps also make little sense and are only "accurate" for some point roughly in the center of the zone. So, if there was "universal time", you might arrive in Phoenix at something that looks like 2200, and it's the afternoon. You might ask a local/hotel clerk/etc "what time do people go to bed here?" if you can't rely on the sun. However, you would be quite certain that the morning meeting is at say 1400, so you set your alarm for 1230 and everything just works!