Track View > Curve Editor or Dope Sheet > Track View toolbar > Scale Keys
Track View > Curve Editor or Dope Sheet > Keys menu > Scale Keys - Time
Use Scale Keys to scale keys horizontally, changing the horizontal location and amount of time covered by selected keys. The horizontal location of the keys represents the frame in time at which the key action takes place.
The scale center for scale time is the current time set by the time slider. You can scale keys about any point in time by dragging the time slider before you use Scale Keys.
To scale a selection of keys horizontally:
Scrub the time slider to the frame to use as the scale center.
In the Track View Key window, drag any of the highlighted keys horizontally to scale, or press Shift and drag to add scaled copies of selected keys.
The scaling effect depends on the direction you drag with respect to the time slider location: