Boss schedules a meeting at 6:30 AM on employee's first day of work after 2 weeks off, reschedules meeting for next week at 6:29 AM: 'They're 3 hours ahead of me, so it's a comfortable 9:30 AM their time.'

They should at least have the decency to cancel the meeting more than a minute before it was scheduled.  

It's not always easy to schedule meetings when half of your team is halfway across the world. If you have a meeting with participants on three different continents, one of the participants might have to wake up earlier than they'd ever want to, the other participant likely has to log onto their Zoom much later than regular working hours, and the luckiest of the bunch gets to have a cozy afternoon meeting. Everyone would prefer to meet during regular working hours, but you can't control the sands of time!

One of the most essential things about scheduling meetings at weird times is ensuring that all participants know about it before it happens. It's not best practice to schedule a meeting for 7 AM at midnight the night before, because attendees might be asleep when the meeting is scheduled and still asleep when it starts. It's essential to give employees sufficient time to prepare for meetings before putting them on the calendar. 

One of the worst offenses in meeting etiquette is canceling a meeting five minutes before it starts. If an employee takes the time to wake up and get to the office early, just for their boss to cancel the meeting that was supposedly mandatory, they might start to feel like their boss doesn't respect their time, and they'd be right! Their boss probably wouldn't be pleased if that happened the other way around.