Note that Fedex does not get address changes filed with the Post Office so I will answer based on a package being re-routed due to an incorrect address.

Re-routing delays are anywhere from a few minutes to a few days. If the corrected address is nearby, then the courier can make the delivery the same day. If the new address is in another, but nearby town, it will take a day since the courier will have to return the package to the local station and it will go out the following business day on the correct route. If it is in another farther away (25+ miles) it will take a day or more depending on the service level paid for by the shipper. Note also that re-routing due to a bad address incurs a fee and negates all service guarantees.