many recommend to start flowering when the plant is 1/3-1/2 of the desired final height. dont forget that the plant will get wider too, they need horizontal space, if you want the undergrowth to get any light love.

it also depends on what strain you're growing.
2 months may be too long.
i vegged mine for 2 months and am ending up with a 5 foot plant that takes up the whole closet.

and dont forget, unless you have feminized seeds, you'll be trashing half of them.

good luck!