Closing time in the regular beer tents is 11pm, so last call for drinks is at 10.30pm. In the food halls and coffee tents, the bar closes at 11pm.
Remember that after last call, finish your drinks as quickly as possible because working the tents all day is hard and all the servers are looking forward to relaxing. Even they have to rest sometimes.
So don’t beg and plead; when it’s closed, it’s closed. You can come back for more fun the next day and raise the beer Steins again.