I didn't know the answer to this either but Curly Mac quickly taught us how long.  About 4 uses!  LOL.  After that, she refused to use it and would go pee on the floor next to it.  I think all the pups are different but I've read several on here who said the same thing as me, the pup won't use it after (?) number of uses. 
I have found however, that she WILL use my new washable pads many many more times before I have to change them out.  I think it's because they really soak up the moisture quickly and her paws don't have to touch it.     |