The rules define the time range as: "Timing starts after character select, and ends at final cutscene."

Just to clarify, does "final cutscene" mean the last gang's extermination cutscene, or the full "city cleared" cinematic that comes ~5 seconds afterwards? I ask because I would assume the latter, but Blues' NG+ run (the only reference) is timed to the former.

Good question, the rules defined here on speedrun.com were made before I became a moderator for the series so I guess I could edit it to be a little more direct. The only recorded run is blues' run, but I would assume the way he ran the game was timing ends based on the full city cleared cinematic after the 5 second dossier update countdown. (his run starts at 00:04 and ends at 23:07 on the youtube video, which is 23:03)

So if I've read everything correctly, the end-time is sticking to when the 5 second dossier countdown ends (what Blues' time is calibrated to at 23:07), and not the absolute end cinematic at 23:29 in his video? If I've got that right, thanks for the clarification.

Correct, the end-time is sticking to after the countdown ends

Reviving this because I've found a weird trick with the ending cutscenes: if you extract after killing the final gang and the 5 second dossier countdown begins, then respawn in The Keep, the true endgame 'cleared the city' cutscene plays before the cutscene for the gang (actually, in some instances I'm not sure it plays at all if you do this), even before the loading screen.

I bring this up because it appears to save ~2-2.5secs, involves technical skill instead of just waiting for 5 seconds, and intuitively I've been thinking this should count as a valid way to end a run, after all it is the true final cutscene (unlike using one of the 'gang defeated' cutscenes as the end-point).

So is it a fair assumption that skipping to the final cutscene like this is legal for the boards?

Edit: I should also say that the endpoint using this cutscene is the first frame of black screen after warping (because the beginning of this cutscene is fading in from black).