Tip: When determining a time limit, remember that players won't be as familiar with the level as you are. If you normally complete the level with the timer around 100, others might run out of time on their first try.
I've realized that you don't have to jump at an angle to clip through, straight up still works:
if mario is $0008 to $0009 units (in pixels) to the right from the block, you can clip through that bottom-right corner.
What happened is that mario's head collision point (this interacts with MarioBelow is not triggering the one_way_down_right [broken], rather the block to the right of it, hence a collision point cannot be on two blocks at the same time, it only picks one. When going upwards far enough, the only way to check this collision is via MarioSide and Headinside as that detects the leftside of the player.