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Time reports > Time reports for payroll
If the report has everything in order you can approve booked work hours. Approving hours locks them for payroll purposes. This will also lock the vacations, which means that they can't be changed.
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When the button is green none of the hours have been approved. Orange means that some of the projects have been approved. When the button is grey all of the projects of the day have been approved. Approving hours locks the notes too.