I never encountered such situation. Generally speaking, the A&R Team should tell you the release date clearly. Besides if they have to release earlier or later they have to inform you at the time.
Anyway... if you already signed a contract with one label, I don't think you can sign the track to another. That's illegal and you should relieve the contract immediately.
But please remind words above are just my personal suggestions, please also consider the opinions of others.
Best wishes for your track!