2012 Greenhouse grow...Light deprived

Hi every one i am back, never really left just been hanging out in another area of the forum..Well i got my 2012 grow all planted and going. And am going to do a light deprived grow this year. I will be coveing the greenhouse starting July 15 with a 10pl black/white black out sheet...It is 50' x 100' and really heavy so i put in some gaments and will be pulling it over my 16' greenhouse with ropes? I have never done any of this so i have some worries...One is how hot it will get in the greenhouse when covered? Also how humid it will get? This is what i am thinking? I can cover it at 6pm and then take the cover off when it gets dark at about 10pm and it would have lots of air flow at night, but at 6pm it might be to hot? So i could cover it at 9pm and take it off the next morn at 9pm? But then it would stay on all night and allow very little air flow at night in the greenhouse, so i could put in a little cage fan under the cover to suck hot air out and feash air in? Or put in a dehumidafier?....What do you guys think?...This will be my 3rd greenhouse grow. This year i pinched all my plants 2 times to get more tops growing, the last two grows i let the plants get way to tall and wasted lots of grow space under the plants...Happy growing.

Why are you covering them? To have them flower and finish faster?

You are eliminating some veg time so the plants will not be as big. Not to mention all of the extra work moving the tarp off and onto the greenhouse.... plus the potential environmental issues. Is this really what you want? I would just let them be and wait until October!