
I actually just won an adaptil diffuser from Discover Dog's facebook page. I have used it next to Nando's crate. Usually he doesn't sleep in it any more and is free to sleep out of it if he so chooses but during firework period I put him in it as a 'den' with blankets over it.
Not sure if the adaptil had any effect as I only started using it yesterday but he pretty much slept through the fireworks last night which is unusual for him.
For 'ideal' results though I think you should use them for a week or so beforehand.