I would give it a good 100 miles or 2 weeks, whichever comes first, before pushing the panic button. If you don't have a good level of fitness, you will probably get some pains. As you increase mileage, you may find that your neck/back/quads are talking to you the next day. That is normal. Cycling is not supposed to be totally pain free. If it was, the bike lanes would be too crowded.