When to initiate flowering?

Hello all,

This is my first grow. Ordered seeds from BuyDutchSeeds. Ordered Northern Lights. I wouldnt know the difference if I received something other than that.

This plant is four weeks old today. I move it outdoors during the day and under a 400 watt HM at night. The plant is currently 13 inches tall and looks to be healthy. Can anyone provide comments on the general appearance. I dont know if this the expected height for a plant four weeks old. How long before I should consider initiating the flowering stage i.e. 12/12?

Thanks in advance!

it depends on how large you want the plant you can expect indica dominate plants to double in size during flowering and sativas to triple even quadruple in size.

Would it hurt to start now?

i would start asap, the longer in flower the harder it will be for the clones to root.