Plant growth nearly stopped and leaves look funny

Hey. I'm a first time grower... literally started May 9th with a seed i found in my bud. I've since started 8 more plants. They were growing great at first but now they've nearly stopped and the leaves look funny on a few. I think it my be underwatering or too much light.

I water twice a week and had them on a 20hour light schedule. I turned the lights off early last night by 3 hours because they looked tired.

Someone please help.

What lights are you using?
I dont think you've too much light.
The plants look healthy enough
By looking at the bottom thermometer in the 1st picture it's seems to be 19 - 20°C?
So it's even cooler at plant level
That's quite cool for cannabis and will slow down growth

Ok so i started watering more, that helped. And i made sure it was a little warmer but now I'm noticing my lower leaves are dying. Is this normal to put more energy towards the developing buds on top? Pics provided.

first of all, there are no buds...

I'm not staying there are buds now. I'm asking if what is happening with my plant is something normal or unusual? I know they are not budding. They aren't autoflowers and I'm not there yet.