Back in the 90s, my father had a method of pre-vacation scheduling. He announced to all his colleagues that X day before he left was the last day he was accepting new work to finish before leaving.

Inevitably, someone would come by the day before he left, and ask him if he could do one more critical thing.

He reminded them what he said, explained he was finishing work others had asked of him, and didn't have the time for their work before he left, but he'd be happy to look at it when he got back.

Next vacation announcement, that person made their requests earlier.

Scheduling has its own cultural mores and Overton window, and there's no "right." If you're unhappy with its current coverage: push it in the direction you want. People will adjust.

You can say "No" nicely and without being an asshole.