Thanks for the file, Michiel.
So far I can see, it was all based on Key-frames and the handles of the F-Curves where all flat. This allowed me to use the Region Tool here.
Before you use it, switch off “Frame Snapping”, as that might delete keys that will “land” on the same frame based on snapping.
To see that in action, have a look to this one minute clip here:
https://www.amazon.com/clouddrive/share/ntzkKzWIi1a4IAWIFIwMXLrsFRMMpLAxMxf076ujZHQ?ref_=cd_ph_share_link_copy
I have not shown your scene here, as I wasn’t certain if that is OK, the Key frames are neutral enough I guess to show those.
So, again, it works for this specific case, any other animation set up or F-Curve adjustments, needs perhaps a different approach. Especially here any XPresso or procedural animation.
To turn a whole scene into an Animation clip might be the way to go, or just use a Time track. each needs an evaluation, hence my request for the file.
If all fails, sometimes the only way for very complex set ups is, to render out an image sequence and reverse this.
If there is any other question, please let me know.
All the best