Until the due date has been reached you will not be able to work with the results of the assigned zApp or zApp Book. There are no restrictions on how long a zApp or zApp Book may be left open.
The default due date is 7 days from their opening date and time. You can ammend this date using the calendar. Due dates can be ammended at any time until they have arrived (Go to MY LIBRARY and select the Assigned zApps tab or the Assigned Books tab and click on the due date). Beyond the due date you can give students an extension by clicking on the green icon with a tick. This takes you to results and you will see the green extension button next to each students name.