It would be great if after a teacher submits/closes a test when time is up, the students cannot continue to work on it. If the test is still open on the student computer, the student can continue to work despite the fact that you submitted their test for them at the end of the class period. Then there is a discrepancy between what the teacher sees for answers/scores and what the student sees.
Other testing platforms I have used close the test down, unless you have added additional time to that student for the purposes of accommodations. When a timer was set on a common assessment by another teacher, we could not override it to allow for students with accommodations for extra time.