Possible causes are:

Overtime calculation is set

Setting "Employee"＞ Employee type setting > [Edit] of target category> Calculate day's overtime work " Overtime start time "」

Working hours that meet the conditions are treated as overtime.

Overtime working hours are fixed

Setting "Employee"＞ Employee type setting > [Edit] of target category> Calculate day's overtime work [Detail] button＞「Overtime start time」

However, if you are registered for a time longer than the scheduled time , the overtime will be counted only after the registered time is exceeded.

*This item counts working hours that exceed the registered hours as overtime hours.

The handling of overtime hours is set

Setting "Employee"＞ Employee type setting > [Edit] of target category> Calculate day's overtime work [Detail] button＞「Extra Hours Work allocation type」

If "Fixed" or "Overtime" is selected, it will be treated as fixed or overtime.

*This item is for setting which aggregate value should be used when overtime work hours (work hours outside the schedule) occur .