My plant a little small?

So this Is my first grow and it's been 4 weeks since she popped out. I didn't have good lighting at first but upgraded and got some good CFL's on her and she instantly grew like crazy but recently it seems like she's slowed down and I'm worried she's way to small for 4 weeks. Can I get some input on this as well as when I should switch to 12/12 I currently do 24 hrs thanks!

Here are the pics!!

i place my seedlings under a 400w ceramic metal halide and that plants size is equal to 12-16 days depending on strain in my setup. also i never use 24hrs of constant light, i notice big jumps in growth during my "night" cycle plus i believe it to be less stressful for a plant because it is more natural to have an evening in the plants life.