Not sure what you mean by "off the heat lights". Are you using some lights to provide bottom heat to the flats? Or do you mean can they come out from under the grow lights?

Bottom heat is needed only for germination, not growing. Once germinated it is lumens of light that becomes vital, not air temps.

If they are getting sufficient light in the greenhouse then they don't need to be under the grow lights, but sufficient light to prevent leggy plants is difficult to do, even in a greenhouse, this time of year, especially as far north as you are.

How many hours of good sunlight would you estimate they are getting daily? 12 hours? Fine. Less? Then supplemental lighting is needed.

Dave

Sorry, I'm using rope light to set them on for bottom heat. Yes they get at least 12 hours of sun light, I think, it's noon here and the sun is still on the greenhouse, the greenhouse is to the east of our house so the sun will hit it for another hour or two (we have no trees around):(

I was worried about the air temp at night mostly. it still get down in 40's.

Here's picture from last year are{{gwi:220639}} they leggy?

They look a little leggy to me. It is not only the length of the day but the intensity/quality of light. 12 hours of day light in the winter is not equivalent to 12 hours of light in the late spring or summer. I doubt that you get 12 hours of day light now. The days simply aren't that long yet. That won't happen until the equinox. When growing seedlings indoors or during the winter, it is generally recommended that they get from 14 to 16 hours of light. You'll need to use supplemental lighting to achieve this a prevent legginess. If you don't mind leggy plants and have been happy with your results, don't change what you are doing.

Air and soil temperature is critical to the development of plants and in particular young seedlings. You don't want them to even get close to freezing at this point. Cool (40 to 50ºF) air temperature is often used as a natural growth regulator.
In general, young seedlings will do best if kept at around 60ºF or slightly higher. This is an optimum and doesn't mean that plants won't survive if the optimum can't be met. Usually, once a plant has reached transplant size the temperature can then be reduced to finish growing the plant on. Yours have barely sprouted and if the bottom heat is all you have to warm the plants then keep them there. If you have heaters then you can remove the bottom heat if you want it won't hurt. Depending on what you are growing, I personally wouldn't want my seedlings or young plants for that matter to be growing in 40º temps, even temporarily. Especially, warm loving veggies or herbs like peppers, eggplant, and basil.