I don't get how that's a better system than not requiring overlaps between timezones that are essentially too far away from each other for reasonable overlap? O

I don't get how that's a better system than not requiring overlaps between timezones that are essentially too far away from each other for reasonable overlap? Other than being good for the employer of course. I do agree that having "core hours" is very valuable with flexible hours. Core hours need to be less than a regular working day though and they should be negotiated by the team internally. Have a team of night owls? Core hours can be 4pm to 10pm for example. Why would you review a 7pm EST PR any earlier than the next day (which is when you'd see it) and your next day happened to start at 10am only that day? Unless you had started your day late or were working later for another reason (like wanting to take half of Friday off) and you happen to see it. Timezones suck and make things slower. Companies need to acknowledge that and not by making people work longer than they should.