After you have set up the general test settings, you can still set up exceptions for some of your students (students with dyslexia, dyscalculia, etc). Also, these settings can be used to give extra attempts if the student accidentally submitted their test, or to give some students access to the test at a different time.
In the Teacher environment, click on the Test tab. And after that, click on 'student settings' to change settings for individual students.
You can, for example, give individual students more time for the test or an extra allowed attempt.
When you change settings for individual students, make sure to select the students it applies to before saving. You can find the list of students on the bottom of the page.
Once the settings are saved, you can see the individual settings under the student's name.
These settings can be used to set a different date for some students, or give a deadline extension. They can be used to give an additional test attempt, or schedule a different start date altogether.