lol no packing bowls is about the least strenuous activity one can partake in... if your friends are too lazy to put some fuckin weed in pipe/bong/bubbler they are probably high enough already...

personally i pack fat fucking bowls and make sure i always light up a nice section of the herb so that i may fully enjoy a really fuckin huge bong rip... thats just me though

as for exactly how long you would light it for it kinda depends on a) how big a hit you are gonna take (obviously) and b) how moist the weed is (if its kinda moist it might take a bit to really cherry well)