Watering properly might help. Soak them good and don't water again until the pots feel light then soak them again. Feed every 2nd time as a general rule.
Reverse osmosis, RO, or distilled water is my preferred water and the only thing I've ever used. Lot of minerals in most tap water that end up causing problems.
Could be your higher temps and lack of water causing the drooping or possibly root rot setting in at the bottom of the pots. That would restrict the plants ability to get the water it needs. If they are perked up when the lights come on it could be that or just the cooler temps early in their day.
Looks like coco that you are growing in? Whatever it is it could use some perlite so maybe add about 20% or so when you move them to bigger pots.
The plants look pretty healthy so maybe it's those big fat leaves just too heavy to hold up that's making them droop.
I found a great spot to download
FREE POT BOOKS . I downloaded a grow bible first and getting some more. Book looks great and complete like the real one I have here. No web site but just a page of links. Just right click on what you want and then "Save Link As" to download so they don't open first as many are 50+ megs. They got lots.