Scale Keys expands or contracts key timing by moving all selected keys proportionally away from or toward the current frame.

(Scale Keys)Use Scale Keys in Curve Editor and Dope Sheet to change the locations and time spans of all selected keys.
The scale center is defined by the current time set by the time slider. You can scale keys about any moment in time by positioning the time slider before you use Scale Keys.
To use Scale Keys:
Select an animated object, then right-click and choose Curve Editor.
The following steps work in both Curve Editor and Dope Sheet modes.
Drag the time slider to the time you want to use as the scale center.
Click
(Scale Keys) or from the Edit menu choose Transformation Tools > Scale Keys Tool.
Highlight one or more keys.
Drag to scale the selected keys or hold down Shift and drag to add scaled copies of the selected keys.
Drag away from or toward the vertical time slider in Track View for the following results: