How much light for the grow phase

[Newb2growing]

Hi as is everyone here apparently this is my first grow. I'm sorry but I could not find this question answered anywhere. I'm using the Roleadro 2nd Generation 600W LED Plant Grow Light Upgraded Full Spectrum Indoor Growing Light . I'm growing traditional feminized plants (white widow, skunk #1, and trainwreck). For the first 8-9 weeks of the grow phase before I switch to a 12/12 how long should I have the light on. Continuous working time suggested is 10-16 hours. I don't want to destroy my brand new light so do I push for 16 hours of light with 8 of dark? I'm open to suggestion. Also for the pH I've heard it's good to vary it but how much difference is it really between 6.2 to 6.5 pH. Will it really make a difference for nutrient absorption in the plant?

Edit: I'm using Coco. I should have phrased it more in that I wasn't sure if the light can handle an 18/6. They freaked me out. I don't want to burn down the house while I'm at work. The room I'm growing in is cool at 72 pretty much always in shade. I also bought fans to keep things cool. THanks for the answers!

[gbauto]

Most people use at least 18hrs on-time during veg. Some folks with auto strains run 24hrs. The lamp will tolerate running continuously as long as room temps are reasonable(below 95deg) so I wouldn't hesitate running them at least the 18.
Soil or hydro???

[St.buds]

Your gana veg for 8 weeks???? Tht will be a fuckn tall ass plant

[Weasel]

What medium are you growing in? That will determine the ph range you use, as I'm sure you know.
The ph scale is logarithmic. One full point up the scale is a tenfold increase. So a ph of 6.5 is 3 times as high as a ph of 6.2. Yes that's a big difference.
Yes it's important to have a range. Different nutrients are taken up by the plant within slightly different ph ranges. Outside that range a plant will not be able to access that particular nutrient and will show deficiencies. For each nutrient there is a slightly different optimum range. Oops said that already
Does this make sense?
I'm sure there is a nutrient uptake chart in GWE somewhere, I'll look around.

But it's not usually up to the grower to manipulate that range. Ph usually rises in the root zone, at least in the growing styles I use. I think in all mediums (?). I haven't grown DWC.
The general approach is to feed on the low end of the range and let the rest happen naturally. For hydro style and soilless that would mean feeding at around 5.5ish. I've tried runs in soilless where I fed some clones at 5.2 and some at 6.2. All other factors were identical. The 5.2 ones were bursting with health and the 6.2 plants were displaying pretty bad deficiencies and very slow growth.

I don't know what to say about your LED. Seems like an odd design that it can't run more than 16 hours straight. I've never had a light, of any kind, that couldn't be left on continuously, as long as you want. If you have to do 16/8 than that should work. I've had plants start flowering at 15/9 so you probably don't want to veg at much less than 15 hours daylight.

* Edit_ ok there are ph charts in this link. http://www.growweedeasy.com/ph#soil-pH

[St.buds]

Vegitation 18/6 flower 12/12 thts standard for photoperiod but not the only light schedules tht work like weasel said and autoflowers can run 18/6 all the way threw