By design the session runs until the last user left the meeting. The way a moderator can manage to kick all the users at once is to terminate the meeting manually or automatically. And this must be done by using the third part application, in this case Moodle.
Manually: When the BigBlueButtonBN activity has been set for opening the session in the same tab, and after the Moderator/Teacher logs out from BBB the user is sent back to Moodle. The page where the user lands shows a list of the BigBlueButtonBN activities
for the course with an End button at the end. If you click that button, an end command will be sent to BBB meaning that the meeting is terminated and all the users kicked out.
Automatically: You can also set up a duration for the meeting. This feature was included for 0.8x to prevent recordings to last forever when one or more users (typically students) let the session open. If you decide to use this feature be aware that there is no way to change the duration once the meeting has been created, and if the meeting was created (meaning that some one get into the meeting) before the time it was scheduled, the meeting could end before the session was intended to end.
To play safe, give the session about 15 minutes before and 15 after the planned time. If the meeting was supposed to be from 10:00 am to 11:00am, give to the duration 90 minutes. So the teacher can join the session 15 minutes before hand and left a little later if needed.