boil down to communicating about the thing that you're planning to do, and describing accurately
Yes, effective communication is very important.
instead of distorting it based on a certain convention (e.g. if you say that we start at 9 but everyone shows up at 10:30 instead
This is a funny example to use directly after emphasizing clear communication, considering how ambiguous "start at" can be.
We "start at" 9, but that's very common language with a flexible schedule. If I went home last night with my earliest accepted meeting at 10:30, nobody bats an eye when I roll in at 10:25.
Perhaps the words you're looking for are "we don't have flexible hours" or "without discussing it with me first, you must be in the office by X and not leave before Y."