Vets say a week but I take mine out all the time, just be careful not to put it down where the local mutts pee and poo. Much better to get them out and socialised, far more are put down through lack of socialisation than ever die from catching something - they get a lot of immunity from their mum anyway.
Another tip even if the vet recommends it don't worm them at the same time - its too much for the pups poor little body to take on two lots of chemicals.