If you are talking about the Trading Places, you need book ahead at the reservations desk. You should have also enrolled in the Romance Rewards. As for days and times, I think it's MWF 9-4. They only take 10 couples a day.
Trading Places is Monday, Wed. and Friday. Book in advance. If you haven't signed up for Romance Rewards, there will be a charge. The bus leaves at 10 and returns at 4. Under no circumstances should you ASSUME the bus will go over if TI is closed b/c of a red flag. It's not a given.