starting from seeds...how long till "the switch"

i started some blackjack and its been awhile since i started from seed...so was wondering how long i should wait till i flower them..is it just about the height or what?

13 views and no input.....bump

yea really whatever is in ur space range because when u flip they can double in size so just try to judge it by what kind of space you have i have done veg for a few weeks then flower which went fine or 12/12 from the seed which also went well