Depending on what option you have enabled in settings, Non-Working days may be counted.
To prevent the planner from counting non-working days, such as weekend days:
Click Access Button
then click HR Admin.
Click Settings, then click on Holidays & Absences.
Go to the field Apply Work Pattern On Other Events and click Turn On.
📌Note: You won't be able to apply work patterns on other events only for specific locations. You have to set the location to all before you action this.