Currently I'm trying the following set-up:

PS4 --> PS Remote Play --> OBS (to record) -->Windows Movie Maker (crop/edit)

How , during any of these stages, can I add a stop watch to the video? Haven't found an option in any of these programs. Would be great to see it real-time of course, but that's not necessary.

Or should I look into some other programs? If yes, which?

Eventually it will probably also be an issue how to cut out loading times? Not with the game I'm currently working on, but any comments regarding that would also be appreciated.

I have a feeling PC runners have it easier. :)

If you’re using OBS just download LiveSplit and add it into the layout in OBS. You won’t really get a good autosplitter to remove loads when playing on a console game - there’s a program that works based on visual images, but whether or not that would be allowed is a per game basis.

Brilliant, works like a charm. Apparently LiveSplit is an absolute standard program in the speedrun community - I'm surprised I didn't find out about it before!

Anyway, thanks man.