If you mean how long before you can harvest, depends what strain it is. If you don't know, then you gotta wing it and observe the rippining of your ladies. Here's a page where nebula explains the process: http://www.growweedeasy.com/how-do-i-know-when-to-harvest-marijuana
As for triggering the flowering stage it all depends on how much bud you want from that lighting and number of plants you have. You might want to wait a couple more weeks at least to get those plants a bit healthier. They look a bit deficient to me that's if the lightings not playing tricks on me and those leaves airent yellowing on the upper branches. At min, I would get them to a foot or two and then trigger. If I was just going with two plants under my 1000, I would at least get them to two feet and lst them.
Yeah they are bit yellow top leaves but that's where I've been spraying them with the hps on and creating heat spots I think