How Big Should I Let My Plants Grow Before I Switch To Flowering??

Hey guys I was wondering how big i should grow my plants before i should switch the lighting to 12/12? Should i let them get as big as possible or what?
I have 2 plants growing in the hydroponic and 1 plant in dirt. let me know
thanks

Depends on how big the flowering room is that you're working with.. It is typically safe to say (depending on strain, of course) the plant will triple in size by the end of flowering.