Graying out fully booked time-slot

Is it possible that fully booked time-slots would be grayed out? For example i have a max customer limit of 10 and when i book 26th of february for 21.00 and 10 customers than the time slot remains open and when i try to book the same time-slot again then AFTER the checkout area i get a message sorry you cant book that time it is already booked. It is inconvenient.

The page I need help with: [log in to see the link]