First off - most joints are $1000/month, though it varies from participant to participant; some I believe are $600. The specific limitation is found on the left side restaurant's listing page. I understand that some are still one visit per month only - that information should appear there, along with which credit cards the place accepts FOR REWARDS NETWORK CREDIT. There are some that will happily let you pay with other than a Visa/Mastercard, but refuse to give miles for anything but those cards.
"Monthly" means calendar month - a $500 breakfast on the 1st and a $500 dinner on the 31st should be fine.