Quicktime Player Custom Hotkey (to re-wind the video by 5 seconds)

I want to create a hotkey on Quicktime player that allows me to re-wind the video by 5 seconds. Essentially, I want to be able to do the thing where one can jump back 5 seconds on a YouTube video by the pressing "j" key.

I have tried to follow this guide. However, it doesn't seem to work. Am I doing something wrong?

Create keyboard shortcuts for apps on Mac – Apple Support (UK)