Ahh, I see it. The correct timing is somewhere a bit after the spike sinks into the ground.
It's so hard to hit though. If anyone who's beaten this thing on very hard could give me some advice I'd love it

EDIT: what seems to be working better for me is jumping right when the final pair of spikes finishes stabbing into the ground.
Also hitting
shift lightly, and not letting go of right arrow.
Never mind, I think a heavy shift might be better.
FINAL EDIT:
WOO! I made the last jump of the corridor three times in a row. That was way way easier than I expected it to be.
1. Stand as close to the final up pointing spike as you can. As in so close it looks like you're on top of it.
2. When the final down pointing spike stabs into the ground press shift and right arrow simultaneously.
3. Watch out for the falling gravestone
