After just 5 "short" weeks I am already noticing massive improvements on the narrow and wide hurdler. I went from hold a strap 3-5" away from my foot to comfortably holding my foot with the middle of my palm on both variations with each leg! Granted my glute is still on a block for balance, but the difference is huge.
What I think has helped tremendously is an intense focus on pushing my knee through the back of my leg (on all of the FSs, really). Concentrating on the correct position pays dividends!
Splits are a 5 year goal for me (I am insanely tight pretty much everywhere), but the reward is in the pursuit so far.