In another thread, I considered the optimal use of PB at battle start.
You'll notice chaining Snaps is less effective than bolstering them first with DK and Twin. Using DK under the effect of PB will apply the DK debuff, while using it from a neutral form will not. If you could fit only 4 steps into PB, opening with DK is still ideal.
Basically, you'll do more damage, more quickly if you use PB to ramp up to GL3 instead of putting it off for Snap spam. It's a different story if you're in the middle of an encounter and want to use PB "just for the damage."
Also, I think it's a bad idea to burn BfB/IR before you're ready to apply DoTs.