Use it every time you water or feed I mix it in a coffee cup in warm water till it dissolves then pour it in your jug.
I wouldn't change your light cycle now wait till next grow. Since your lights are on in the day keep your door open if possible a good flow of air will help the temps but you need to get them down my room is 78 degrees lights on with rh at 48 to 56 depending on if I water or not and light out I like it cold about 65 or lower if I want to bring the purple out. You can poke holes in the top of your pots and use string to tie some branches down and open the canopy up just go easy lol.
And last but very important grow what you know.... order seeds from a reputable company (the vault, herbies or midweeksong) do not order from haze.io dudes a douche bag. try some white widow x big bud cross by 00 seeds it is a bad ass plant or moneymaker by strain hunters both very very easy to grow great results with a 8 week flower time. Some strains take up to 12 and 13 weeks or more to finish and that's just to Damn long. Looks good my friend and my last bit of advice is don't get anxious let your plants finish get a loop or download a microscope app on your phone to check your trichs if you have no access to that wait till your red hairs start to retract and curl in you will have lower leaves starting to yellow and read the curing forums the weed when cured right will be twice as good.