When you set up the breakout room you can click on Settings in the bottom left of the breakout panel to change the length of time for the breakout room to close and give time after it closes for members to come back to the main room. Set the time for the rooms to close 2 minutes before you want them to close and then set the timer for 2 minutes. This will display an alert for the members of the breakout room that it will be closing in 2 minutes and should work for you.
