What happens during the underwriting process for a FHA preapproved loan?

I was preapproved for a mortgage, we found a builder put down a deposit and had the house built. Credit history established-score of 674. I have sent in all of the conditions required. How long does it take for them to make a final decision? I personally spoke with the underwriter and she said that if all conditions were met and satisfied, then the closing should occur next week. I spoke with my mortgage specialist and he said that I will definitely close before May 1st. I sent in the information 2 days ago and have not received a phone call or anything from either of them. Anyone have a similar experience or advice?