How long will a male keep producing flowers?

[Rusty Trichome]

Ive read about 3 weeks into flowering but I know not all plants flower at the same rate.

True. It's really up to you. How many seeds do you want. (rhetorical question...no need to answer)

If you pollinate too early, you may only have enough of the pistols available to make a few grows worth of seeds. (one pistol + 1 grain of pollen = 1 seed...1 pistol + 100 grains of pollen = 1 seed)
If you wait too long to pollinate, you'll likely get shitloads of seeds, but may be forced to do a partial harvest of the mature (seedless) buds, while the seeds finish. Whichever way you do it, be sure to allow the seeds to completely mature. Sux going thru all this and getting minature seeds that aren't viable, but explode violently when accidentally packed into a bowl or joint.