In the absence type, you can select a time credit and mark it as sick leave.

Title
Give the absence type a descriptive title here (e.g., Sick Leave or Vocational School). This name will be displayed in the time tracking calendar and reports.
Time Credit
Here you can specify whether the employee will be credited with working time when using this absence type.
The “Balance Daily Schedule” option credits the employee with the missing working time to reach the daily scheduled work time, provided a scheduled work time is set for that day. The options “Half-Day Scheduled Time” and “Daily Scheduled Time” credit the employee with the respective portion of the daily scheduled work time. If no scheduled work time is set for that day, no time will be credited with these three options.
If you select a fixed time credit here, the value you entered will always be credited whenever this absence type is used.
If “None” time credit is selected, this absence type will not affect the time account.
Count as Sick Leave?
If you select this option, the absence type will be counted as sick leave. The reports will include a summary of the employee’s sick leave within a calendar year. Absences marked as sick leave will be displayed in a different color in the time tracking calendar.