Progression of the Treatment for Parvo?

I took my puppy I bought from Petland in for his shots, on Friday. Later on that evening he seemed lethargic. Saturday afternoon he had some diarrhea. I called the vet and was told those were normal reactions to him receiving shots. Monday morning he was throwing up clear foam, and had clear diarrhea, but was still eating and drinking, the vet said he should feel better by evening. Tuesday he seemed a little more active during the day so I assumed the vet was right. But by Tuesday night around 3am he had explosive bloody diarrhea and vomiting, refused to eat, and only drank with lots of encouragement. I set the timer on my phone and got him to drink small amounts until the vet opened at 7am (I was waiting in the parking lot for them to open). They weighed him and he had lost 12 pounds since his appointment on Friday. I left him at the vet's office to run tests and give him IV fluids, and medicine for the nausea and diarrhea. An hour later the called and said he tested positive for parvo (he has been vaccinated, that was one of the shots he got in Friday, his second to the last one in the series). I went down to see him before they closed for the night to check his progress, he wagged his tail when he saw me, they said his vomiting had stopped. But he was still having explosive bloody diarrhea. I went in again to check his progress this morning. They said he got a fever during the night, and was still having explosive diarrhea. They are keeping him again tonight. But tomorrow I will need to pick him up before they close at 4:30 because there will not be anyone there to care for him over the weekend. Is it safe to bring him home? What I can I do to make sure he stays hydrated at home if he still has the diarrhea? How long does Parvo last? (Today is day 6) what are the signs that he is improving?