How long is "normal" for flowering?

Seems like 10 weeks or so is what everyone says for how long plants should be under 12/12, but I'm averaging more like 15. That is until the hairs are all NOT white and the trichomes have developed well. Is there a way to speed it up, that I'm missing? Second year of growing legal marijuana here in Montana, so I've got the process down pretty much. I grow in sunshine mix #2 soil, (2) 400w hps covering a 3ft X 4ft area, BC "recipe for success" nute schedule, well vented, 70-80 F temps, humidity runs a little low.

Give it as long as it needs to complete flowering, the only thing you can do to speed it up is make sure all the conditions are optimal, beyond that there isnt much you can do, thatd be cheating. Anymore than 15weeks would be a little abnormal, if it needs it it needs it

The strain makes the difference in flowering time. Try an Indica to get shorter flower times.

Have you checked for light leaks? They will elongate flowering.

Also, you might just be growing plants that take a long time to flower. I have heard of plenty 15 and 16 week sativas.

Yes you can speed it up. But the amount of time will be strain specific (as is the actual harvest time). If you use Busmaster right away and then use Ultra Snow in your nutrient mix and Canna Boost via foliater you will add weight and you will also take between 1-3 weeks off of your flowering time. For example, if I am growing a strain that finishes in 9 weeks, I will be ready to harvest in around 7.