I think most people wait two weeks, but call your vet and double check. If your vet doesn't know they can contact FARAD for you:
http://cafarad.ucdavis.edu/FARMWeb/
http://www.farad.org/
Good luck and I hope your flock gets better soon. :hugs
@Mtnldy's Gurlz
Welcome to BYC!
Which one do you have? If it's the package that is 107 grams, and the active ingredient is Sulfadimethoxine (look carefully, a there is a similar one called sulfamethazine), I think the dose is supposed to be one teaspoon per gallon.
-Kathy