Time distortion changes the length of time required to playback a clip in your composite. These operations generally fall under one of two categories: retiming and warping.
Retiming is the process of slowing playback by adding frames, or accelerating playback by subtracting frames.
Warping is the process of slowing down, speeding up, or even reversing playback on a clip without necessarily altering the overall length.
TIP: When working with temporal operations, it helps to attach a Viewer to the retiming or warping node so you can see the effect of your changes.