Heat mat?

How long do you guys keep plant on heat mat
?

I'm not sure if this is what your talking about or not: I use a heat mat for my rooting tray and I leave it on 24/7 with a 100 watt cfl. I leave them in that tray for about a week or so or until I have about 4 sets of leaves and the stem is about an inch or two tall. Then I put them in my system.