Do's and don'ts on test day?

It can be as quick as 10 minutes. But this is what happens before you get to Quant:

1. You read the instructions
2. They collect your signature
3. They take your ID
4. They take your picture.
5. You get your locker and put your stuff in there.
6. (in some instances) if there are people ahead of you, they accommodate them first.

Then you have the AWA and a 10 minute break. So it's well over an hour (assuming you take full 60 min for AWA) before you see a quant question.

Can you take a longer break if you don't need the full 60 mins for AWA?

Not officially. But remember, it's not a full hour that you get. You get 30 minutes for the first AWA. If you finish early and move to the second essay, you get another 30 minutes.

Do you plan on doing warmups during the break? I'm not so sure they'll let you do that.

I would say that if you do a few questions that aren't extremely difficult, it might help get you in the groove, but if you encounter really hard ones, you could freak yourself out and kill your confidence.

If you've already truly learned the math formulas, grammar rules, etc. before your test day, then it wouldn't hurt to review a cheat sheet as a reminder. I have a photographic memory so if I do that, I'll remember how things looked on the page even if I'm having trouble remembering how to solve the problem. But if I don't really know the material, I can easily confuse myself by doing that. I easily got As on all my psych quizzes in college by memorizing the review pages for each chapter. LOL.

On a related note...as far as your diet goes that day, eat a higher protein, lower carb lunch to keep yourself mentally alert. If I eat a tuna sandwich I am sharp the rest of the day. Pasta, and I need a nap. A good snack for breaks: an apple, a small banana, a granola bar, a protein bar, something like that. A mini Snickers bar is good too...a burst of protein without too much sugar.

And don't load up on caffeine if you don't normally have a lot already.