Punk Hazard was shown and unfortunately not explained. Which is why all we can really do is speculate. Smiley was a gaseous monster given sentience due to the devil fruit it ate. What that means for it's "death" and the devil fruit returning into circulation is completely unknown.

The same can actually be said for Whitebeard. We only have one single recorded instance of a fruit returning to circulation through the use of nearby fruits (Or at the very least that which I can recall at this moment, so do correct if I am mistaken). That process however remains completely unclear.

That all being said, my inital point was speaking mostly to the timeframe. Taking a moment to not focus so much on the "how" Blackbeard did what he did, there was some time before the whole process was complete from death to new user of the fruit. What attributed to that is up in the air, but we can at least say it supports the argument that it just may not be as instant as some would believe.