I'm a ways down the list, so I told my new boss that I would let him know when it's even getting close. As for an exact number of days, it should be in your contract. You could always contact HR and ask them how many days notice they give you to show up when the recall occurs.
Good luck to you, I hope it works out for you. I wish I had your problem.....I hate my new job, and can't wait to get called back.