Re: work requirements - depends on the school. Some schools won't even let you work ten hours a week. Check with the school's financial aid department (they generally know the rules on this). Of course it's going to be different if you're a PT student or something.
Re: December 1st - this is from the National Association for Law Placement (NALP) principles. Maybe it's ABA too, I dunno. But here's from their principles and standards:
D. Summer Employment Provisions for First Year Students
Law schools should not offer career services to first-semester first year law students prior to November 1 except in the case of part-time students who may be given assistance in seeking positions during the school term.
Prospective employers and first year law students should not initiate contact with one another and employers should not interview or make offers to first year students before December 1.
All offers to first year students for summer employment should remain open for at least two weeks after the date made.
You can see more rules from NALP here: http://www.nalp.org/content/index.php?pid=16#part3