To "Hotel California" - "You can check in any time you want but you can never leave".

That's always the problem with some chinese employers. Contract don't mean a damn to them. It's best to resolve the matter with them but stand firm. If you let them have their way they will probably take advantage and come up with loads of other craps which is not stated in your contract.
The curfew as you say is not stated in the contract signed by both party, so tell them to take it or leave it. Walk if you have to, they will have a hard time finding teachers if they don't give in.

Most chinese believe that once you are on campus you are safe. They do this because they have a reponsibility to ensure that nothing untowards happen to their students and staff. It might be so.

But then again, the safety thing most chinese schools talk about are all bull. They place security guards only at the entrance and some of them hardly ever patrol the campus, and by 1100pm "scooby Do" will be snoring in his pen. What bloody safety are they talking about. Security in chinese school is meant to prevent people from leaving but not preventing intruders from intruding.