Hi HAIR boy...
The determining factor, when considering plant size, is
HOW much light (lumens)
How many plants (quanity)

SOME STANDARD EXAMPLES

You can flower 9-16 plants nicely in 1-5 galon containers using a 400-1000 watt HPS liight

If you are growing 16 plants (1 gallon containers) you should flower when the plants are 6-10 inces tall with 4-6 nodes.

If you are growing 9 plants in 3 gallon containers you should flower when the plants are 10-14 inches tall 6-8 nodes.

If you are going to continue to clone you may consider cloning your plants when they are at the desired height.. lets say 10 inches.. clone it down to 6 inches.(topping the plant)
...and then let it grow for 5 days
...and then FLOWER..

iloveyou