The Retimer tool lets you generate output footage at a frame rate that is different from that of the input by retiming the image using the Warp interpolation mode. This uses motion estimation to generate intermediate frames, or Blend interpolation mode which generates a weighted average of adjacent frames. The Warp mode provides significantly better quality. Additionally, motion blur (temporal anti-aliasing) can be added so that moving objects appear blurred, as they would when filmed with a real camera, which has a finite shutter speed. You can then modify the timing and/or speed curves through the Animation editor in the UI to create a constant or non-constant time warp.