How long can I wait with traveler's diarrhea to see if it goes away without seeing a doctor?

Traveler's diarrhea. Unless the diarrhea is severe enough that you are getting dehydrated, you can safely wait 2 weeks to see if it goes away by itself. Warning signs of a possibly more serious infections include blood in the stools, fever, and severe weakness. After 2 weeks it is best to consult with a physician.
About one week. Most "travelers diarrhea" will resolve on its own within roughly a week, however it can improve more quickly with a short course of antibiotics (cipro) plus an anti-diarrhea medication such as Imodium (loperamide) ad. Any blood or mucus in your stool, fever or more severe abdominal pain, or persistant symptoms should get you to see your doctor.