I’ve done some testing, and turns out you can buffer a spin from literally any state in the game. This includes bonking, jumping, crouching, going through a loading zone, rolling, etc. - as long as you end up in a state which allows you to spin, you can buffer the input at any time.

The biggest time save that I can see from this is from spin-jumping, then groundpounding and pressing Y as you land to start a roll at maximum speed. It’s also good when you need to make a high jump right after collecting a moon.

I’m not a speedrunner myself so I can’t say how useful this will be; I just noticed that it could be done and figured it could help.