My contractor just poured the concrete and set the posts for a new fence we are getting and much of the work was done in the pouring rain. Will this hurt the concrete and effect how it holds up down the line?
All concrete sets up under water. http://www.cement.org/cement-concrete-basics/faqs
The only thing that will be impacted is the finish. If the top was not covered then the concrete will take on a bumpy appearance as the finer material may wash away and expose the aggregate.
ACI 301prohibits the placement of concrete in rain without "adequate protection".