Sorry I don't know anything about the time periods and all, but here is our story.
DD came down w/ strep this past Wednesday. We took her to the Dr on Thursday and her quick strep test came back positive. (All it really took was one look at her nasty throat and we all knew what it was! YUK!) Anyway, she just laid around Thursday and the Dr. said she could go back to school on Friday. However, she made it about 1 1/2 hours there, ended up w/ the school nurse calling to come get her. She stayed w/ her Grandparents and threw up several times. She ended up having to miss a birthday party that night (on of her best friends, she was so upset), but she started feeling much better Friday night, even keeping some pizza down. She felt pretty good on Saturday and was back to normal yesterday.
We are leaving for DW on Thursday of this week, so I was glad we got it treated quickly. I would just keep a close eye on your DS and take him to the Dr. w/ any concerns. (all DD did was complain a little of a sore throat) FYI...If he does come down w/ it, don't forget to have him finish all the medicine so it doesn't come back!!!
Have a good trip!