I can pull off the glitch semi-consistently by jumping just before I hit the ground and as I hit the ground, because there's an input buffer.

Molehole said that the human limit is approaching, and while that may be true, I've just found a skip in lvl 5 that saves about half a second. once jumping off the top two blocks of the breakable wall, by timing the jump through the wall (It's VERY precise) you can just barely jump off the top of the third block, and cling the block in the corner. This block is positioned above the lvl exit, so it saves time because your falling into the exit, instead of sliding into it.