I collect as soon as they are ready to start dropping the pollen. But the female pistils (and their respective calyxs') need some maturing prior to pollinating, or you won't get many seeds. I 'paint' the pollen onto the pistils of lower branches when ready. (4th week of flower, minimum) Turn-off fans, segregate the plant to be pollinated, and don't sneeze. Remove pollen container from flower room and either store the rest of the pollen, or rinse well in warm-soapy water to kill the remainder of pollen. Do not foliar spray for a couple of days, or you risk killing the pollen before the tube (pistil) transports the pollen to the calyx. Water drowns pollen.

Not the most ingenious solution, but here's my isolation chamber for males:
If they get too tall, I just top 'em. Takes a week or so to recover, but this allows the females to mature a tad more with minimal risk of widespread pollination of your entire crop. Would love to find a 4 foot long 10" tube of plexiglass to replace this ghetto set-up, but this has worked very well over the past year or so of use. :thumbsup: