Your MBs will stay activated for charging privileges until midnight of the day you check out. You'll be fine using them for breakfast and lunch and anything else you want. You will not get a folio of that day's charges, though.
Your account is settled during the night time before you depart, unless you have hit your charging limit (assigned by Disney; usually based on the level of resort you're staying at), in which case it's charged when that happens and the balance starts all over again. If you are concerned about the amount you're spending, a credit limit, a low balance, etc., your best bet is to stop by concierge every other day or every three days to review your folio. It's also a good idea to use a regular credit card and not your debit card for many reasons.