The point to holding the smoke within our lungs a longer time is that more seconds within should = more time to absorb. And while that's true, most bio-adsorbtions don't all run at the same speed throughout, and you get a funny kind of diminishing returns. In other words, the smoke chemicals begin by crossing into lung tissue at a super-fast rate within the first two or three instants, then absorb more modestly over the next few seconds, and then finally barely adsorbs at all for however long you may keep it held inside.
So, the first few seconds gets you an 85% amount of the chemicals absorbed, an additional few seconds more only boosts the absorbtion another 5% or so, and it might take a minute to get another 5%. That's what we mean by diminishing returns; the extra holding time didn't really give you much better delivery, so why bother?
For those readers who are biochemically trained, I suspect that the speed of smoke aborbtion is a function of the inverse square law for seconds held captive, just as a guess [Vesperae has such training & I don't know how many others here as well].