Since you seem to be growing a photoperiod strain and not an auto flowering one, you will have to change your lighting schedule to 12 hours of lights on and 12 hours of lights off to initiate the flowering cycle. Once you change to 12/12, your plant should show signs of flowering in 10-20 days time.
Once you change to 12/12, you must also leave it at 12/12 right through until harvest, which can take anywhere from 8-12 weeks on average.
I would be switching to 12/12 asap, otherwise things are going to get very crowded. Great looking plant though!
Hope this helps, Organoman.