I haven't done the full research on this, but regardless of group, isn't the amount of races the same each year? What I mean by this is that no matter when we stop the timer we skip the same amount of time at the end anyways. The time it takes between you passing the finishing line and you having seen the "cutscenes" should be exactly the same length of time irregardless of which rallies you've been racing.
To me it seems more exact in to stop when finishing and not the guesswork of waiting for the cutscenes.
After reading this I reached out to the developer to ask if we could get this feature. The only answer I've gotten so far is " at the moment you could modify the career save file for those years to: "Status": 1" I haven't looked into it as of yet but I will at some point.
At what points should I start and stop the timer for career mode? I would say the timer should start when picking the car for the first year and the stop when you reach the finish line for the last stage.