Bah, a few seconds is plenty. If your smoke aint doing what it needs to do in that short time you need to invest in some new herbs.
Think of a cigarette, do you see people holding in their drags to get a better nic fix? No, you just cough and feel sick. If you in turn just hack and cough due to holding your hit you're going to just waste it anyways.
How enjoyable is hacking until your eyes pop out and your neck has so many veins popping out you look like a hard on with arms and legs?