Volunteer time is precious, so the format has to do more than put people in a room. Students arrive with uneven questions, and mentors often have limited context. A small amount of structure helps both sides.
A useful session can start with a shared topic, move into two or three student questions, and end with written next steps. The mentor does not need to solve a whole academic path in one sitting.
Structure is not bureaucracy when it protects the student’s chance to be heard.
The best office hours create momentum. Students leave with language for their next email, a cleaner project idea, or one concrete revision to make before asking for more feedback.