Hello there fellow marijuana enthusiasts, I am new to the grow culture and have built a indoor RTW system, proud papa of 3 out of 3 seedling, the little girls (feminized)are 23 days old today, having some concerns on when to start flowering. Lots of info to choose from and I’m new so it’s got me swimming a bit. Any positive support is very much appreciated. FYI using 800w led full spectrum, coco coir medium , begain coco A and B as well as cal-mag. Mixing at 1/4 and given 24 hour light. Have timers installed and running c02 4 hours day. Have Nitrogen pad in room and they seem to be very happy and hardy, ph has been stable at 5.8 to 6.1. However they seem to be a little short compared to photos I look at in this stage, is that norm. I will post photo at next visit. Also have started schedule of 3 min feeding once every other day 2 3 min drinks Ph water every day. Thanks for any input
being that they’re feminized seeds you have the luxury of choosing how long of a veg cycle you want and when to start flower. According to my fox farm schedule the minimum they show for veg is 4 weeks. I however usually do at least 5 to 10 weeks. It gives me lots of time to do some topping and low-stress training, while allowing plenty of time for plants to recover etc.
Welcome and I hope you enjoy growing! You are around a lot of like-minded people and not to mention the pros and members of this forum are outstanding. Post any question you have. Have a nice morning. 
PS keep in mind that once you start flower it’s not uncommon for your plant to double in size. So make sure you leave room between lights ceiling Etc
In my current grow, I switched to 12/12 at six weeks from when it pops out of the ground I am going to try seven for my next grow.
I have my first scrog on the go and I went a bit long but was at almost 11 weeks when I switched. Probably be a bit less next time. 
Also my first attempt at flowering clones /monster crop as well. But it’s all a learning curve. And as @neckNflu said everyone is more than willing to help if needed. We’re all here for the wonderful herb. 