Hay there man, how you doin....
Sounds to me like you been doing your research, some!....
You can top your plants after they have a min of 3 shoots,
But it is more fruitfull to wait till it has lotza shoots....
I personally top my clones right after they start roots in the cloner!
As for topping or pinching....
if you want more shoots then top,
if you pinch and fold them they will just straigten out unless they are tied down!
I personally us pinch/fold method to keep my flowering ladies the same hight...
Now onto your lights...
doing the clone/veg stages at 24 or 20 or what not hours is kinda a waste of power!
Them young ladies Don't need or Use more then 18 hours worth of light,
This all comes down to personal preference
In the flower section i would run 12/12....
Running a shorter on period is OK at the End of the plants life,
Not before!
Using a shortened light cycle will just stress the plants into thinking it's the end of the season!
Hope that helps ya some.....