Waiting until the result screen sounds needless since you already beat the game when you beat Genos.

I'd say in favour and sake of ease, the final hit on Genos should count as the timer ends(or the load to the result screen), as that is also when you lose control over the character and only have menus left to sift through to give you an overall idea of your performance. (we use RTA and not IGT)

Thoughts on this?

i'm fine with it being on the black screen after you skip cutscene like you did on your pb, but on genos last hit is not going to happen, black screen gives you more time to split correctly instead of reaching for the split shortcut while still doing the fight

I'll agree to that. The black screen makes more sense as it also loads into the results screen. Besides, the boss kill glitch might make the final hit on Genos for awkward splitting. I've tinkered with it and it would result in a different fight. That would reinforce the black screen split moment.