The waiting period part of the Brady Law has sunset. All that remains is the "instant" background check. However that can, in theory, result in up to a 3 day wait, IIRC. However it hasn't for me and I've bought 4 firearms since then, (plus one right before Brady went into effect (1911A1) and one (serious social purposes shotgun) right before it began to apply to long arms. Only bought two subject to the check though, the others were from private sellers, not subject to the law. The two checks took less than an hour each, how much less I'm not sure, since I wandered off to look at more guns. :) (both at gun shows).
Of course YMMV depending on your state. Some states do have waiting periods. And bans on things the federales do not.
And what if an attacker shows up during that time? "Excuse me Mr. Rapist--would you mind coming back in a couple days when I have my gun?"
Also, please explain why people who are so dangerous they must be prevented from buying guns are not so dangerous that they belong in prison, and why the freedom of such people should be put ahead of the freedom of the law-abiding.