Well, you can challenge the curfew.  First, I would absolutely send your landlord a letter by certified mail (and the same by regular mail with certificate of mailing) asking where this "rule" is written.  Advise your landlord that you have read your lease with a fine tooth comb and that this provision is not included in your lease and was not the basis of the bargain in your renting the apartment in the first place.  Advise him that there is no attachment or rider to the lease that indicates this "rule" either nor is it posted in a conspicuous place ANYWHERE in the complex.  See what happens.  Then seek some legal help.  Good luck.