As long as the cause of the blisters have been removed then I would say about 3 days before they are no longer sore, I always draw a piece of wool on a needle through the blister to drain them or cut the blister open but leave the skin in place to offer a bit of protection. the sooner they dry up the sooner they heal.
I can recommend Compeed plasters. I have only ever had one blister and have only used just the one compeed plaster, but it was brilliant. Make sure you get the right size for the blister in question.