What time is a good time for everyone to show up for a face-to-face layoff meeting for a global company?

If you don't do it simultaneously, you're going to hear by rumor rather than by official email, which is IMHO worse.

If you do it simultaneously, everyone will know something is up, because there's never simultaneous global meetings.

I agree. But, IMO it's what you should expect going to work for a giant company. It's a machine, it does not care about you. Some of the people will care about you, but often their influence is quite limited. It's important to understand this at the start.

I'm sorry but you work at Oracle. Terrible people. Very rude people. You should expect it.