I guess the first question is whether they included an out clause in the contract that outlines the expectations for giving notice? Mainly, have they said a specific time frame (two weeks, four weeks, etc) and are there any blackout dates (i.e. not within seven days of the first public performance, etc).
I'm hesitant to give any actual legal advice here (not being a lawyer after all), but I did have my brother (who is a lawyer) look over a contract I once had to break. In that case there was no out clause outlined in the contract, so his advice was that a standard two week notice was sufficient and the company could not challenge that, which they had initially threatened to do when I gave the notice (which was three weeks before rehearsals were scheduled to start). Again, this is just anecdotal and if you are truly concerned I would suggest consulting a lawyer in your area, as laws can differ from state to state (my situation was in Ohio, for the record).