Jen
I am at MOC now, but getting ready to check out so I won't be able to answer any further questions you may have immediately. The waterslide is open from 9 am to 5 pm and the height requirement is 42 inches. My daughters did see the slide attendant enforcing the rule, but to be balanced, my kids weren't on the slide that much so I can't say if it is enforced all the time, or just by specific attendants.
BTW - the pool is open before/after the waterslide closes. Not sure of the time it stays open at night, but we swam till 8 or 9 pm on some evenings and there were no problems.
Enjoy your stay at MOC - we did.
Rick