You can lock the time span between two markers to move the segment in time, without scaling or adjusting the shape of the curves within.
To lock the time span between two markers:
Activating the Lock option disables the adjustment of FCurves within a segment as you drag the retime markers.
Locking a segment of animation is useful when you want to retime multiple keys together, without adjusting the shape of the curves. Once the segment is locked, drag the markers to shift the entire segment to a new location in time.