When should I call back?

I was made an offer of emloyment (on the phone and in writing) that I accepted on August 13. This is for a position to start on Sept 8. The offer is contingent upon the company's extensive background and drug, criminal check. I received a call from the background company last Monday afternoon and resolved the issue with them and the employer on Tuesday. When accepting the offer, I asked how long it would take to know for sure if everything was clear. The HR rep said as long as I didn't hear from her, I was fine. She also said she would send an email with last minute reminders on where to park, which entrance to use, etc. I asked how long the background check would take and the HR rep said 1-2 weeks depending on the county. This Wednesday will be 2 weeks. I received a call for an interview at my 2nd choice and have the interview scheduled. I really want the job that I accepted the offer from and wondered how long I should wait before I check to see that all is well and I should head to work on 9/8. I guess in this case its no news is good news but it sure would be nice to know so I can cancel the interview with choice #2.