I’ve been waiting until the top inch or two of the soil is dry before watering each time, which is what I’ve always heard and adhered to the few times I’ve grown in the past with no problems. This time round my plants look best when they’re pretty much dry then as soon as I water, bearing in mind I still don’t give so much that there’s run off, they look over watered within an hour there’s perlite in the soil and clay pebbles in the bottom half of the mix to try and help with aeration, not really sure what’s going on with them?
They are starting to look over-watered. You can tell by the wrinkling on the larger leaves. Have you tried weighing the pots before and after watering? At that age, they can stand to be a bit drier before they need water.
Ive been waiting until about the top 1/3 of the soil is dry which has been ok for me in past grows but seems to be a bit soon for these, pots are always light as a feather when i water them, ive never actually weighed them with scales though
Your soil may have gone hydrophobic. Rather than absorb moisture, it repels it and the water just flows right through. How much do you water regularly? While the top may be dry to the touch, the bottom could still be wet. I get the same droop at lights on but once I have given them their normal load, they perk back up within the hour. I’ve also found that some plants from the same strain can exhibit their own preference.
I would follow @canagen advice. The best way to really know if they need water and the amount is to weigh them.
I do that, and also wait for the soil to be dry not like 100% dry, but most of it, and then I water again.
there’s perlite in the soil and clay pebbles in the bottom half of the mix to try and help with aeration, not really sure what’s going on with them? 
