Oh dear a single digit post count!!Welcome to the other side,grass is colorful and smelly on this side
My fellow newb (im just wait...uhm....30 somewhat days into veg of my first indoor grow) your temps at night are at "Will cause stunned plants" and "Growth might seem to slow down significantly" level! most people say 59F is good i will totally up that to 64F for fast growth and a cozy environment !
What strain is this lil baby? Photoperiod or Autoflowering? and what medium are you using? Do you have meters? (Ph,Ec)
Most people will stick to 18 hours of light and 6 hours of dark during veg state for Photoperiod Plants and 24 hours of light - 0 hours of dark for autoflowers since they will flower in their time no matter what!
Too much light for a seedling is about 8 inches away from a 400w MH bulb,which i don't think you have provided!!
If by too much you mean hours and not intensity then you are in for a surprise as cannabis plants in veg state will take up ALL the light possible,it's the flip to flowering TIME CYCLE that causes the plant to flower and grow buds (or balls if it's a dude).
The 12 hours of light you mentioned on a daily basis will cause the plant to start flowering prematurely and lead to something that has become a tact for people that grow 10 or more plants at a time using the method called SoG! 12/12 from seedling will make you loose yield if you don't know your ABC's instead of assist in any way!
You will need to provide a minimum of 13 hours+ of light to avoid flowering early and keep the temps between 59F(lowest night temp) and 80F (highest temp at day) making sure your max difference from night to day is equal to or less than 30F,again i note,the DIFFERENCE between the two temps!
Have you read GWE's
Begginer Guide ? It has provided me with what i mostly used in the start (Ofc the forum members have provided tons of awesome information along the way)
Worry not matie,we will be here on your every step,just avoid meeting
for a couple weeks till you get branches,he will teach you the way of the blade!!!