Do not try to force flower. The only time I would suggest force flowering is when you are growing a long flowering sativa. Usually most plants will tell you that they are ready to flower by showing preflowers at their nodes. When you first see this sign then you are good to begin flowering. Usually you don't have to force flower so much anymore cause a great majority of strains have a lot of Indica in them nowadays. Wait till about week 4-6 (as mentioned earlier) and see if anypreflowers have shown. If not then give it one more additional week after week 6 and then if no signs have shown you can go ahead and flower. Also, you will want to consider the fact that most plants can double and even triple in size during flowering so you may want to measure your grow space and see if you have enough room to contain all the plants. If you find you don't have enough room the go ahead and flower. Hope I was some help.

Happy Toking :rasta: