how long do i flower

ive got my plants on 12 hrs now for 3 weeks now. they was grown from seed so is it 8 weeks from putting the lights to 12 hrs or from when i noticed they was fems. i have 1 ready to harvest now but i was given that and i knew it was female. thanks

Different strains have different blooming times. Any photos? That would help us help you. It really depends on how the plant looks and what you want the trics to look like.

theyre blue cheese

You should invest in a £2 30x jewellers loupe off ebay, this will allow you to look at the trichs (google it if you don't know what I'm on about).
A general idea is when most of the pistles have turned brown/red/orange but it also depends on what kind of high you want.
8-12 weeks is an estimate on most strains

cheers mate thanks for everything