If someone wants to see him, they are told to call and set up the meeting when they can see him tomorrow. So if you want to meet with him next Friday, you call next Thursday and say “Can I see Mr. Buffet tomorrow?”
I love the simplicity of the rule: I can see you today if you asked me yesterday, but I can’t fill up my schedule any further in advance. This way he can determine how he wants to spend his time within the context of the next 24 hours instead of booking things weeks or months in the future. Now his schedule is relevant instead of prescient.
I’m sure many people will say “well, he’s Warren Buffet so he can do that”. Yes he’s Warren Buffet, but no one granted him the power to do that or say that. He decided that.