4-5 week from pollination takes seeds to mature.
I just harvested a seedy plant myself. I let it flower till I saw some amber trichromes and then harvested (wanted to get some smoke out of it too). When I harvested after 8 weeks of flowering most of my seeds were mature and are now already growing into new plants!
You can know if the seeds are mature by their color and the stripes on them.
white seeds with no stripes are not mature and have 0% to germinate
tan/brown seeds with stripes all over them are mature seeds and have a high % to germinate