Here are some useful tips from ProVideoCoalition.com thanks to Trish Meyer. The first tip is about re-timing key frames.
Tip 1: Retime a set of Keyframes
Ever have a bunch of keyframes that you want to spread out in time or condense in time? Select them and press Option on Mac (Alt on Windows) and drag the first or last keyframe in the group. This will retime the set of keyframes “accordian” style. (Note that the middle keyframes may end up on partial frames in time, but this is rarely a problem.)
When retiming keyframes, place the current time indicator where you want the last keyframe to land, and add the Shift key after you start to Option+drag (Alt+drag) and the last keyframe will snap to the current time.