Classroom sessions have an initial maximum time of 2 hours. Though the teacher can add additional time, up to a total of 7 hours.
This can be done easily by selecting the 'Time Remaining' button in the teacher dashboard.
Though the available options only add increments of 30 minutes at a time.
If you would like to add more than 30 minutes you can manually type in the end time of the classroom session in the 'New End Time' window.
For more information please visit our 'Sessions' article here.