Well intense sunlight that young will stunt them alittle... heat means nothing its moisture. Since they use the water to get nutrients heat will only make you have to water more often. There is often 10 to 20 days after a seed reaches surface that humidity is more important then light intensity. The plant at that early stage uses the humidity to start photosynthesis by turning humidity into usable moisture. I choose to mist my plants rather then water every 2 days... I can water every 3 -4 and mist daily. By misting your promoting humidity and the plant uses the water that hits it directly instead of via soil absorbtion. Key thing here.. I stop misting at day 30 in veg....before I 12/12...If your not going ot use a propogation plastic dome thing or party cups with plastic wrap you may want to try mixing in direct clean ph neutral water misting bottle.
I edited to remind you that you can burn plants by having lights to close after misting. its a magnification thing... I use a pvc pipe cut in half and have t5- t8 on movers i just move the light up to 6 inch for an hour or so also helps them stretch to the light.