Is there a federal level 3 day waiting period to buy guns?

In all the years I've been active here, I've never heard this discussed.
A guy on another forum claims that "We already HAVE a waiting period to buy a gun".
He's a "negotiator-type" - willing to give up some rights for things that would personally benefit HIM - like "I will happily pay $200 tax on AR15s to GET national carry."

He's a "staunch supporter of the 2A" and has said "Fudd-like" things many times, and when something was said against mandating a waiting period to buy, he had NO OBJECTIONS - "because we already HAVE a 3 day waiting period at the federal level - it doesn't affect most people because the background check is instant, but by law, they have 3 days to deny, but after 3 days, they must sell if you haven't been denied."

Does that make any sense? Any truth to what he says?
Maybe he's twisting something around?
There are way more laws than I can keep track of.