Difficult to be sure without pics but have a look at the bottom of the pot- you should see a few white roots poking out of the soil. If so your seedlings should have enough of a root system to cope with the MH.
Start the MH a good height above the plants, say 2.5 or 3 feet and move it closer by increments so they can get used to the powerful light. MH gives off a lot of heat.
More info would help especially pics . Feel free to start your own thread
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