30-35 days from initiation of flower... there is genetic variety, too.
It also doesn't just stop.. it tapers off at end.
if it becomes a problem, snap stems about 6" below where you want the cola height... support it the first 24h or so, but after that probably have to hold it down. The colas will turn upward regaining some height, too. if the stretch isn't done, maybe go a bit lower so you don't have to snap them a 2nd time. Put a little thought about it so you can snap down all of them without too much overlap or congestion caused.
when done right, the leaves don't even wilt, but if there's a bit too much vascular damage, they may get droopy the first 24-48 hours. Weaking the stem before you do this can help. The other thing to worry about -- if the stems are too rigid, it won't 'snap' well without severe damge or even completely severing -- there is no fixing that, lol.
that light looks like it runs hot (not the color, just the type of light is lower efficacy = greater heat production). Affix it directly to the ceiling as long as you don't think it'll damage the canvas with heat or start a fire, lol. Can probably gain a few inches that way too.