This is basically all Revenge of the Sith spoilers, so read on at your own peril.
The second to last scene of Revenge of the Sith features Darth Vader and the Emperor overseeing the construction of the first Death Star. Several things imply this takes place some time after the main narrative.
- The Star Destroyers have been remodeled.
- The Republic Navy has transitioned into the Imperial Navy and received new uniforms.
- Vader has gotten used to his armor and the Imperial officers have gotten used to Vader.
- The frame of the Death Star is partially built.
How much time has passed?