I don't remember seeing anything on this here. But you could try searching!
The only time I have seen a rewind function or timed backward jump was for Replay TV using VLC.
The version was 0.8.2 and the author gave a methodology for making the change. Try searching Replay TV on the web and reading the documentation.
In Hot keys: Shift Left, Alt Left, Ctrl Left and Alt Ctrl Left are designated as backward jumps starting small and moving to larger jumps.