Hi. I'm new to GOG. I have pre-ordered the game "Destroy All Humans!" which is to be released on July 28, 2020. I've made a few searches but I can't find anything. I'm wondering what time of day this game will be released on the 28th. Are they usually released at midnight or noon US Pacific time, or something like that?

It varies often, especially with highly-anticipated public new releases. But the most common time is between 9 and 10 AM US Eastern.

Thank you!

If GOG gets to decide, the typical time for releases, sales and other important events is 1 PM UTC/GMT. That'd be 6 AM PT.
If the publisher decides, then of course it's whenever they want, out of GOG's hands.

The most common time for updates to the store is 15:00 CET, that's almost always when new sales are started. New releases can be then, or a bit earlier or later. The one thing that's certain is that it always happens on the hour. If it's not 15:00, it could be 14:00, 16:00 etc. So no need to wear out F5.