They should stop stretching around the 4th-5th wk, and start looking a lot like bud during wks 5 & 6, and then they really swell up the last two weeks.
Sometimes everything happens a little faster tho. My Blue Widow should come down this weekend which'll make 8 weeks of flowering, and I thought for sure that this one would go 9/10 wks just because it's blueberryXwhite widow
If you wanna maximize your yield indoor you gotta do some sorta plant training like topping/fimming/LST to keep the plants stout.
But you gotta start all that early on and often!