We also teach on Saturdays = We have 6 days cycle.

You can set 6 days in menu "School - Number of days".
If you are using day's names, then the sixth day will be automatically named accordingly (e.g. if your timetable starts on "Monday", then the new day will be automatically named as "Saturday").

See also:
We need Day 1, Day 2... rather then Monday - Friday
Can I rename the days?
How to change weekend to "Friday-Saturday"
We use 7 days cycle in timetable but we need a free weekends (online).