When in Periods you are able to
Like in the previous section Days, you will be able to simultaneously edit many dates and employees by pressing the 
button. It enables you to select several employees and dates with the same registration, at the same time. This is very beneficial when managing several users at a time, e.g. holidays and vacations.
If the box next to Update only? is checked, then only the days already registered as work days will be changed to the chosen status, instead of all the days within the selected period of time.