Quote Originally Posted by Gandalf_The_Grey
2-5 seconds. THC is absorbed almost instantly, and holding your smoke in is just adding extra tar and carcinogens to your lungs. I'd advise releasing about 2-3 seconds, as you'll get about 80-90% of the good stuff in that time. If you hold a good 5-6 seconds, you'll get that tiny extra bit but at the expense of your lung's health. Some people will tell you they get more stoned holding it in as long as possible, but that's just because they get a head rush from the lack of oxygen (which really isn't good for you). And that headrush only lasts a couple minuets anyway.
Yep, thats the answer your looking for.