I don't think the company would necessarily have to tell the employees what the local office hours are. (I mean, they'd probably want to, just as a matter of leaving nothing in doubt; but it would be no big deal.) If you were born and raised in Manitoba, you are already used to the fact that the local businesses open at 1400 UTC. Of course, if you move to Ontario, you'll have to adjust that. But then, you'll also have to adjust your internal clock to get up an hour earlier too. In that sense, it's more natural than the status quo.

I don't think the company would necessarily have to tell the employees what the local office hours are.

"Only" in job requirements, company policies, employee handbooks, etc. Office hours can also appear in brochures, advertising materials, service agreements, etc.

Right. When's the last time you saw a brochure/ad/service agreement that said "We are open from 9-5, whichever timezone you happen to be in"? On the contrary, here in the US at least, it's much more common for such things to say "we are open from 9-5 Eastern time. [If you don't live in the Eastern time zone, you'll just have to do the math accordingly.]" This might not be improved much if at all under the above proposal, but it certainly wouldn't be any worse.

I don't buy this line of reasoning at all. The idea that a company large enough to have offices in multiple timezones would make a single blanket statement about work hours to all of its employees worldwide is preposterous and bizarre, like something out of a badly-written episode of Dr. Who. The way such things actually work in the real world is, a given employee's immediate supervisor tells him what time he's expected to be at work. If the numbers given to an employee in Chicago are different from the numbers given to an employee in London, nobody would even notice much less care.

The larger problem with switching away from timezones is the mere fact that it's a change from the current system.

As with any deliberate society-wide change, people who aren't so bright (of which there are many) would have a hard time getting the old system out of their heads and learning to use the new one (UTC presumably). It could be done, but it would be difficult on approximately the same order as switching to metric. (The benefits would be much greater than for switching to metric, but, unlike with that switch, individual countries would not be able to receive the benefit from switching unless everyone else, or at least most everyone else that mattered, switched too.)

I don't buy this line of reasoning at all. The idea that a company large enough to have offices in multiple timezones would make a single blanket statement about work hours to all of its employees worldwide is preposterous and bizarre

It's your prerogative to disbelieve me, but it's done.