Slow growth in tent

unless your house is extra cold, probably don't need a heating mat. If you get one, they 'can' help with constency of how long it takes to sprout if the medium is too cold, otherwise. Get one with a thermostat control, don't be cheap. 76-80F is great. I only use it while they are in a tiny seedling pot. I grow in winter and house is 68-70F which means a moist or wet substrate is even cooler due to evaporation effect. I wouldn't use one in the summer. So, whether or not you can use one really depends on context. The medium will be a bit cooler than atmospheric temps, so just use common sense on that one. don't remove leaves. did you ask or mention doing that before, or am i confusing 2 different people? bad idea. Removing leaves is almost always a negative effect and gauranteed it slowed you down in a context of only cotyledons and first serated leaves existing so far. Less is more.. those compulsions or anxieties that drive a need to do 'something' should be ignored. This plant looks like it is getting too much light... reduce temporarily until it demands more. The resulting node spacing on new growth is your guide to adjust light intensity. If it's received too much light for too long, it may be in shock and take some time before normal growth resumes. When it does, yoo very likely need to amp the light back up... use node spacing as your guide.. too lanky, increasy.. too tight, decrease. Once it's mature you won't adjust much after that except to adjust distnace from canopy relative to vertical growth of plant. 80F/50% is a bit of a high VPD, but that won't cause any problem as far as stalling the plant. Seedlings are more delicate than a mature plant. if using atmospheric temp, shoot for 1kPa VPD (reference temp and RH on VPD table) or just below. Leaf temps are cooler, so it works out well. VPD tables generally give suggestions for stage of life, too. Also, becareful of moving an indoor plant into the sun. the sun is much stronger and no loss of intensity from top to bottom of plant as it does indoors. Plus, you risk bringing in pests and molds. It sounds like a nice idea but should stick to one or the other.

After looking at all 3 of your diaries, you are doing something fundamentally wrong......all your seedling seem to be in trouble and changing light or humidity will not fix the issues. It seems you may have cooked them all by using unnecessary "humidity domes" and maybe suffocated them as well. Honestly, I think you would be better off starting again, autos have a very limited veg period and all these are way behind already, meaning you are going to end up with tiny plants flowering in a couple of weeks time. Deeper pots for root development are important and not using clear plastic pots is also important. You don't need a heat mat, and spritzing them with water is not ideal either.........deep water to ensure water gets all the way down to the bottom of the pots. "Spritzing"/spraying only moistens the top surface of the pot..........roots will be 2-3 inches deeper down and missing out on water, meaning they can't access nutrients either.

She needs a little higher humidity. Try to reach 70~%