This works only for absences announced by parents (or students with activated accounts) via quick messages when they use the "Absent" type quick message.
Access "Center management" > "Kinderpedia modules" and click on the settings icon for "Daily Reports and Timeline".
Here you will find the option "Mark absences as approved if there are reported absences". Simply click on the dropdown menu from that option and select the minimum announcement time for the absences so that they get approved and click on "Save".