mmm, i was under the impression that they would not sell with a delay. a guy at work got a delay and they gave him some paperwork for an "extended" background check. there was fee associated with it like an additional $35 IIRC. he has not been back to academy since.
They will not sell if they do not get a proceed. You can get delayed at Academy and if NICS calls back and gives them the proceed they will do the transfer. But if NICS does not call Academy back with a proceed or if they miss the phone call because they are too busy they won't do the wait 3 full business days and transfer at their discretion. That's why I prefer a local FFL that knows me and that I have done business with.
90% of the time NICS never bothers to call back on me so it's usually wait 3 business days then the FFL does the transfer. Back in September I bought a Seekins precision lower and about had a heart attack when they gave me a proceed right on the spot I was fully expecting to just go back to RD and on Friday and pick it up.