After three pretty harsh noob attempts to kill my girls (can call them girls officially as of this AM), I ended up at about 6 weeks before I switched to 12/12 lighting (about a week ago give or take a day or two).
I was all about tracking this or that at first, but after the stress of fixing my awful mistakes, I gave up on tracking anything. It's been smooth sailing since then. The best advice I can offer on this topic is to check out as many journals as you can find. In particular, check out two pictures:
1. Picture of plant(s) at the time they were switched from veg to flower.
2. Picture of plant(s) after the stretch.
This is important (for me anyway) to know how much veg you can get away with. It would be a shame for a body to grow a nice plant only to run into the lack of space issue.
Both posts above are correct, and you seem to have some room, unlike my 36x20x62 inch tent. Good luck, and I hope you grow some amazing stuff.
*Pistils! Pistils everywhere! I woke up this morning, had some eggs and a beer out on the deck and I didn't think it could get any better. But then I saw pistils! Hell, I may have another beer!