Does tapping Z to stop the block selection help or hurt in Mario Kart 64?

I'm not sure if there are any probability differences by pressing Z, but here are some things to consider:

• If you touch a block that guarantees you a blue shell, you might as well press Z to get the shell sooner. Since you are guaranteed a blue shell, even if there is a statistical advantage of not pressing it, it makes no sense in this situation.
• If you are near the finish line and trailing behind someone, you might as well use it sooner rather than later, since getting something (anything) and using it is better than wasting time and letting it select something for you, which you can't use since the race is over.
• If an opponent has a ghost, it is better to press Z and use your item immediately so that they can't steal it.

From my experience, you are more likely to get items like shells, lightning bolts etc if you are trailing far behind. Banana peels and the occasional green shell if you are up front.

So to answer your question, i would say it is ambiguous.

From my personal experience, getting an item sooner in MK64 has a big probability-skewing effect - I've gotten Golden Mushrooms and Lightning while in second place with it, which I'm pretty sure isn't supposed to happen. Back when I played it a lot I actually had the suspision that stopping the roulette early would skip the "what position are you in?" check and just give you whatever the roulette showed. I don't remember it working in first place though.

The randomization function for the game's items in MK64 is run when you press Z or when you let the roulette finish. You'll get a "random" item no matter what so it does not make a difference whether you wait or not for which item you get (at least that human can control).

Some extra info