I just do 12 to 12 because im a pothead and its the easiest ro remember haha
LOL ... classic
... +Rep for the laugh ... stoner !
Just , To answer your question , It's better to stick to the light times and keep them regular , you have the right idea about having them off at the hottest part of the day and i can see that you are thinking about maybe giving them a bit more on a cooler day ... But try and avoid that , It takes plants a while( Not sure exactly how long ...but not long ) to adjust to a light cycle , If you alter it it may confuse them .
Try and think of the seasons ..winter less light ... spring a bit more ... summer LOTS ... fall a bit less ( POW thats when the plant is reciving chemical signals to tell it its time to flower ) .. So altering times on and off ( more and less ) may confuse the signals and you could end up with a tranny on your hands
19/5 is way more light than the plant actualy needs in veg .. you could quite easy reduce that a bit and save electic AND the plant may ( or should ) actualy grow a bit more , Im sure you know by now that a plant will be happy to just sit there if it has loads of light for long periods ... less light makes it go looking for it
I hope i answered this correct and it makes sence