Yes you just gather the pollen when it falls. i use a white peice of paper cut a slit in it, to slide itunder the base of the plant between it and the pot. When lots start to open i'll tap it on the paper when i am harvesting it. You'll know it's time when you see it happening.
4 weeks is the min for a seed to mature, if you pollenate a lower branch early by the time the top buds finish the seeds will be NICE and ripe. Fairly fail safe really.