hi dime...

if you started your plants from seed... which I am fairly sure you did... it really does not matter if you flower them at 4 inches or 8 inches... they will grow to 18-24 inches... even if it is an indica
why?

well... a plant that is started from seed can not be forced to flower until it is "mature"... so they will just keep growing until they are mature enough to flower even under a 12/12 light regiment...

clones are different.. they can be flowered at 1 inch tall and they will only double to quatruple in size...

iloveyou