I've seen all kinds of speculation, and 10 pacific is the least-likely.
That's what, 18:00 in CST? They're going to have folks stay late at work, in August, to a support a release, and make Europe have to wait all day?
Midnight PST is not speculation I've heard, but that makes the most sense to my mind. It's 8/3 for most of the Americas, and it's just an 8am start for the folks supporting the release, and it's not a disaster of a delay for Europe.
From what I've heard, and don't want to be true, it's likely because seemingly Stream updates games at that time.
It's even 19:00 in Belgium then. Would be a horrible work day for Larian... and me xD