Just make sure to inhale. I usually break my weed up into little BB size chunks if im using a pipe. With bongs i leave them a little bigger.

I dunno ive heard holding your hit 4 seconds absorbs 80% of the THC.
The whole thing about the THC getting absorbed instantly is, wouldnt that make hotboxing pretty much useless. I think the highest ive ever been was when me and 3 friends hotboxed my moms car and i always kinda thought it was because of the hotbox.
Anyway it would be cool if someone could find some reliable source on how THC is absorbed into the lungs and how quickly. I'm to lazy to look myself.