I did no tests with permanent timeshift plugin, but normally there should be no problems using it.
It would be great if someone can test it. If there are problems please inform me.
I did a short test.
I have always PTS active, it does not show up as PTS is active, I think this according to your plan
After I removed PTS from the box, i had to make timeshift active.
I'm not sure if standard timeshift always is running, but i had to start timeshift manually.
Then the 2 menu items you discribe are in the recording menu.
I tried "Save timeshift file in movie directory", and after 2 minutes I zapped away.
Then I got the question "stop timeshift?"
After I clicked yes, the program was put in the movie directory.
I do not know if all of this is according to you plan.
Personal I think that time shifting must always run on the channel that your watching, no need for manual starting timeshift.
In the recording menu there should be an option to save the timeshift, by that I mean the program you are watching from the moment you zapped to it (maybe limited to the last 2 hours or so) until the moment you click "save timeshift".
The timeshift must keep running after the save.
There don't have to be any warnings, if you zap away you probably do not want to save the timeshift, otherwise you have a useful Learning Moment, "THINK before you zap"
If you got this working, then you can think about working with markers and / or to be able to save a part of the active timeshift file or to build a small library (say the last 5 channel timeshifts, auto save after zap and remove the oldest) and the possibility to save individual files from that "library".
More option possible, the sky is the limit.
But this is my opinion about this subject, others may differ