Remove the screen and let them do their thing. You don't have much veg time lift but read up on how auxins affect your plant growth. Also look up apical dominance while you're at it
Forget about the co2 and like others said lay back on the nutes. You don't want to over fert and when you decide to up can, scourge the root ball by using a razor and slashing vertically to promote some root growth
You can wait until the next watering. Or just lift your pot and see if its light. I've had to water in the am and pm because it has gotten so hot in my area
Some people will use led or cfl on the sides but I suspect with the reflective material inside grow rooms, adding ore lights just meansore power being used.
Also you don't have to harvest the whole plant at once. Some people harvest buds when resdy then keep the plant going to harvest buds on...
I believe some strains will begin to preflower based on age, not just on photoperiod. I have one blue dream that's probably in its 3rd week of flowering outdoors while 2 are barely going to start to flower.
I planted all 3 towards the end of April and by mid June they were showing their sex.