how long is flowering stage

i been flowering for three wks lookin good but when to harvest

Yea, thats a problem I'm facing sometimes.
Sure depends on the strain but basically I harvest when plants are most beautiful. When I start to salivate just by looking at them...
Nice, hard buds that seem to be slowing their growth with hairs turning brown...

The flowering cycle can take from 6 up to 10 weeks depending on the strain your growing, like pterzw says harvest is dont when about 60% of the hairs have turned brown, but that is only aproximately, to really know when to harvest you will have to buy a microscope with about 50x at least and look at the THC, They have to be amber/Cloudy color wait till at least 50-75% have turned amber.

Keep them flowering for at least another 4 weeks. You won't get a quality smoke if you don't.

thanks guys sites like this is how we have good shit to smoke in the world