Markers Retimer 
Use Markers to move and retime keyframes in the dopesheet/timeline. It will scale the keyframes between each two markers. This is especially usefull for retiming motion capture. This operator is available only if at least two markers are created.
In the dopesheet or graph editor press hotkey 'm' to add markers. Normally you would add them to all the important poses, where you want to adjust your timing. Turn on Markers retimer. Use the markers to adjust the timing. You can still add and remove markers. However, If you want to adjust the markers without influecing the keyframes, then turn off Markers Retimer, adjust the markers and then turn it on again.
Markers Retimer works also with multiple objects and multiple layers by default, if you don't want to use specific layers, then mute them.
Multiple objects
Markers Reimer used for all the rig layered actions, and door and toolbox object actions.
Tip
If you want to retime only specific keyframes and not everything, then use selected keyframes checkbox in the Filter Tool Properties
Note
Unfortunatly Blender's Markers do not work in subframes, but the keyframes will go into subframes during Retiming / Scaling