If you have an open Zoom meeting for online office hours, you may have run into a problem where the meeting automatically terminates after 40 minutes of inactivity. This is normal behavior, there is no way to override the behavior, but there is a work-around.
If you have a Zoom meeting open, but no one has joined the meeting, the meeting will stay open for 24 hours. If someone has joined the meeting and then left, the meeting will terminate after 40 minutes of no activity.
To avoid the automatic termination, after someone has left the meeting, and if no one else is in the waiting room, end the meeting and then restart it. That will restart the 24-hour clock for the meeting until someone joins or you manually end the meeting.