It varies widely, anywhere from 2 weeks to 3 months isn't unheard of. Most are flexible with dates and allow you to schedule your own though, so as they come in you should be able to adjust your work schedule accordingly.
For me, it ranged from two weeks to two months - like others have said, difficult to predict. Two of my II's were pre-scheduled for me by the respective schools, so there wasn't much flexibility either.