The more the better of course. If you can only get 8 hours, make sure you know what you are getting into before signing up. If you can only document 8 hours with a provider (MDA, CRNA, AA) but you have worked in and been exposed to the OR environment, you should be fine. Otherwise I'd personally spend some more time.
It's not just a school requirement. It's designed to help you make a good decision. Besides that, good grades in tough courses will help you, as will healthcare experience. No one thing trumps the other.