Job offer on the spot now what?

Hello, I am wondering if anyone can give me any advice about getting offers on the spot. I am a NG with several years of healthcare experience. I went to a job fair one month after getting my license and was able to interview for a job doing just what I wanted to do. I met with a manager, the clinical manager, her supervisor and a recruiter. I was offered the job, told what I need to wear, my schedule, pay, and when benefits would kick in. It has been a week and I still haven't heard from HR. I was told that if I hadn't heard by a specific day to e mail the recruiter, which I did. He said that it would be a few more days because they have been very busy. So I guess my question is, how long should I wait before I contact them again? I was originally told that they wanted me to start this coming Monday if they could get everything done in time; if not on the following Monday.