I've now submitted a run with a time of 4:20.217, and using the new timer feature I decided to try to split up the run by section. The run has three intentional deaths and two unintentional ones, but fewer movement errors than the 4:23 run. I chose a cat at the end or start of each section to check the timer at, and here's what I got:

Overworld (white): 0:49 ("this way to more cat planet!") Forest (green): 1:52 ("factory!") Factory (grey): 2:47 ("wow, hot lava cave!") Lava (red): 3:28 ("solve the mystery of the gate!") Underworld (black): 4:20 ("good job!")

The sections took 49,63,55,41,52 seconds respectively. Then I re-watched the run and evaluated my mistakes. I don't think the overworld can be improved much, but the forest was awful and there are probably 5 seconds could be saved. The factory and lava sections were what made the run, so I think at most two seconds total between them could be saved realistically. Finally the only real mistake in the underworld was the death which lost almost 3 seconds. So, the best-case scenario splits would be something like:

Overworld: 0:49 (49) Forest: 1:47 (58) Factory: 2:41 (54) Lava: 3:21 (40) Underworld: 4:10 (49)

So while it would be a tough feat to actually achieve 4:10 or below, this does make me think that sub-4:15 could be in reach, and now I can check the timer during a run to see what pace I'm on. Adding more deaths to the route could save another second perhaps, so I do think that a human could someday get sub-4:10.