If, after adding a ‘user override’ rule to a Moodle quiz, you received the following message:
check that the activity you are adding the override to is visible to students.
Also, if you are using time restrictions (eg. for when a quiz opens and closes), ensure that these have been set under the Timing section of the quiz settings and not under Restrict Access.
Add your timing restrictions to the appropriate section of the activity.
Do not use ‘Restrict Access’ rules when using ‘User Overrides’.