Curling serrations along leaf margin, heat related?

There's definitely a little heat stress on that plant. You can tell by the way those serrated edges on the leaf blades are curling up and inwards. It's not very severe in this case and it should be of no major concern. It should clear up after a few days once you raise your lights. I've had this issue a few times myself. Another side note I should mention is that Coco Coir grows are notorious for calcium issues. A calcium deficiency could leave the plants less resistant to heat stress. Be sure to be on the look out for any calcium deficiency and make sure you're also providing enough calcium for the cation exchange and not just the plant. I should mention that calcium issues can arise not just from low concentration but low pH too. It can be difficult to correct calcium deficiencies in flowering. This may not be the case and I suspect you may have simply had your lights a little close but I thought it would be worth mentioning as it's a very common problem to arise for novices. Another thing you could consider doing to make your plants more resistant to heat stress in future grows is introducing a hydroponic silica supplement into your nutrient solution recipe.

Light or heat stress. Certain nute problems can manifest this way but are less common. Make sure your pH and EC are good in and out. If they are, assume it's the heat/light stress and that you have fixed it.