breakout room--host wants to extend time

There used to be a setting when I would assign people to breakout rooms that allowed me the option of either closing the rooms or extending the time they stayed open (beyond the original time I had set). This was a great option because sometimes I wanted to extend until a group finished a task. However, I cannot find that setting and when I host now the rooms auto close at whatever time I had set without any option of extending. Please help me know how to reset that extension option. Thanks!