Terrific thread about MM here:
http://www.disboards.com/showthread.php?t=1675403
Sunday, Tuesday, Thursday, and Saturday are when it is offered.
The MM on your ticket is not of consequence when you're staying on-site; you'll be given the charge slip that Boise mentioned, which is a flimsy little piece of paper that is all important.

Charge food and merchandise back to your room with it, and get in for MM with it (and the ticket of course, for admission). You can see why they made it a small piece of thin paper, yes?
And yep you get it every day during your stay that it's offered (including, they say, if you get there mega-early, the day of check-in, and the day of check-out (easier to do than check-in day, LOL)).
When we checked into PP last Sept, the CM even gave us a sheet of paper with lots of info on it, including that, and even told us exactly what days we would have MM (or EE, then) during our stay. Helpful!