When can i put seedling under 400 mh

Hey guys. Just wondering when a good time to put my seedling under my 400watt MH my seedling is 2 weeks old roots popping outta my 1 inch starter cube and has well second set of leaves. I am doing a ebb and flow hydroponic set up. What height over the plant should i put the light i was thinking about 2 feet.

Put it under now. Height should be about 2-3 feet. Move the light closer as the seedling starts to get stronger.

Thanks man

Does this same rule apply for a 1000w MH? Or should it be higher, and how high?