Notch is the fifth Master Stage from both Super Monkey Ball 2's and Super Monkey Ball Deluxe's challenge modes.
Notch includes a long platform leading up to a moving ovular object with two large holes taking up half the width of two opposites sides of the stage. The goal is on a platform high enough that when the oval is on its side, it is just in line with the platform.
As you may be able to imply from the description, you need to be on the side of the oval that allows you to go the highest up to get in the goal. To do the stage, you want to start rolling at the 57th second and get on the main part of the stage from the left aiming to the right to get around the first notch, and then you want to quickly navigate to the center of it and move along slowly towards the center and stay there so you can get up to the platform. Something to note is that there is a very slight height difference between most of the oval and the platform, so you may want to be a bit back from the platform when you get to the optimal time and then quickly go forward to get on to the stage.