the directions that come with a Volcano vaporizer say to hold in your hit about 10 seconds. they also say only to take in about half your max capacity.
that was always my standard for holding in a hit regardless of method, my friends all agree as well for the most part. only the shit talkers disagree, and for some reason they are all dumb anyways
not trying to diss anyone in here who disagrees either.
another thing i do, is make sure the smoke isnt stuck in my mouth or throat. i inhale just a bit of plain air right after my hit to make sure it gets down deep enough.
im a very high tolerance smoker, i have certainly tested these theories!!