In my opinion the plants are very healty...from the store, the plagron royal mix need to be fertilized from the 40th day....i put the plants in the final pot with royal mix 3 weeks ago. Do i start with nutrients or not? they ever be watered with no nutrients.
Like the project/experiment ;) with the lights. You can definitely start feeding and it's highly suggested you do so now to help those fruits develop. Start at a 1/4 strength from recommended dosage of whatever you intend to use and week by week increase. You should get a PPM meter if you don't already have one to document how much you are giving. I'd also recommend you raise your lights as they look way to close and you will soon see signs of leaf curl or burnt pistils.