In order to meet the DPS check, you will need absolutely maximized stun time on all of them, and they need to remain in cleave range of each other. Ideally, this means every wave needs an assigned Hammer of Justice for each valk. This is YET ANOTHER reason why you bring 5 paladins. The prot paladin will be speced for reduced CD HoJ and can get every wave of valks himself, and the two holy paladins and two ret paladins will each pair up and alternate getting one Valk every other wave. The reason you use HoJ is that it is the longest stun in the game that can be instantly applied when all the valks are all stacked together when they first land and are in cleave range. Kidney Shot, the other stun of the same length, requires too long a ramp up time to reach full duration, and should instead be used as the secondary stun on each valk following the HoJ expiring. Note that the paragon comp, in addition to having the 5 paladins, has 3 rogues. This means that each valk wave looked like this:
Valk 1 (HoJ from prot pally -> Kidney Shot from Rogue 1)
Valk 2 (Hoj from holy pally 1 or 2 -> Kidney Shot from Rogue 2)
Valk 3 (HoJ from ret pally 1 or 2 -> Kidney Shot from Rogue 3)
The final stun after the kidney shots all expire would be a simple holy wrath from one of the ret paladins.