Don't sweat it. ATF audits happen everyday. It happens every 4-5 years according so a few dealers I know. The fact that his took six hours shows that he does not sell that many guns. My LGS recent audit lasted 6 days overall. The ATF takes names of buyers of multible types of firearms all of the time. Hell, my name was taken back in 2008 but I have not heard a word from them. As for him telling you to come back on the 18th, is him not want to fill out the multible purchase document for buying more that two hanguns or receivers in a 5 day period or something like that. Just do what he ask for now and walk away and find a new dealer when you get all of your items. He can refuse to do the transfer if you push to hard forcing you to pay for shipping to another dealer.
Good Luck
Good Luck