generally speaking, if the breeder you bought the seeds from has an estimated flowering time posted for the strain you bought... I generally add anywhere from a single week, all the way up to an additional three, possibly even four weeks (especially for Sativa dom strains) to the breeders advertised flowering times.
I do this because most major breeding companies use high powered lights. Much higher wattage than what I use. This may not apply to you though because I don't know how many watts your running or anything else. Reason I add weeks to the breeders advertised flowering times, is because I'm only running a single 150 HPS for flowering. For veg cycles I just use some high wattage/lumen 6500K CFL bulbs. They get the job done for now.. plus it helps with my electric bill too.
But yeah, generally.. the lower the watts your running, the longer the plant will initially take to fully ripen/flower/develop.
Plus, the extra weeks also assure that my buds are fully ripe, hairs have all wilted and receded back into the calyx and the calyx is swollen, most trichs are either very dark and cloudy and or amber colored (some strains, especially Sativa dom strains, their trichs won't always amber up, once they go dark & cloudy, their ripe enough for picking) and it also assures that the terpenes (responsible for the buds taste & smell) have had more than enough time to fully develop.
hope that helped you out.
peace.
