#local_gradelock
This plugin schedules a task that runs every hour to lock grades after a certain period if they have been edited.
This is so that people with moodle/grade:edit but not moodle/grade:lock cannot change the grade after that period.
Change $TIMELIMITHOURS in classes/task/lock_grades.php to change the cut-off time. It defaults to 8 hours.
Only tested on Moodle 2.8.