If there is an unseen emergency and you need to administer a test over more than one day, at the end of testing you should selected those students and move them to "Locked Status". You can then "unlock" them the next day of testing so they can continue the test.
Do not score rubrics/tests until the students have "Finished" the test.
Here is a link to the related Help Section in Performance Matters:
https://unify.performancematters.com/help/Content/core/sam/olaStudentAdmin.htm
Here is a great under 5 minute video which may help you:
Manage Online Testing with OLA Student Admin - performancematters