When to lower mh after seedlings?

I have just started a growbox 3Lx1.5Wx 4H. I germinated the seeds directly into the soil and 3 days later they are starting to poke through. I have A 400 watt mh hanging at about 3 ft above my seedlings. My question is when would i lower the light to about 1ft above the plants? Is this something i should do right after it grows its first pair of leaves or should i wait for it to grow out a little more?

like you, i start with a 400mh at about 3' or so. usually keep it there for a couple of weeks unless the plants start to stretch. stretching is a pretty good indicator to move the lights closer, but do it slowly. remember its springtime in your garden and if you try to rush into summer your babies will burn