There is significant variance in population per timezone, and even more significant variance in internet-usage per time zone. Much of this variance is just demographic, but most of it is actually geographic. An interesting and convenient thing about the present layout of the world is that the Pacific Ocean takes up almost half of it, and almost half of the world's land masses are uninhabitable tundra and desert (that's not so relevant to time peaks though).

This has the great effect of lowering the median travel times and information transmission latencies between the world's population centers, and it means that for at least this geological epoch; we're always going to have daily global peak and off-peak times for human-driven activity.

A reasonable approximation is to model a sine wave per region with peak amplitude based on typical usage patterns. For example entertainment services will peak in evenings and at weekends, business services will peak during typical core hours Monday to Friday. With enough users spread across enough regions you never have a good time for all users so in practice it is better to engineer things so you can do deploys / maintenance whenever is best for the teams working on the service.