We use 7 days cycle in timetable but we need a free weekends (online).

If your school uses other than basic 5 days cycle in timetable - let's say 7 days - then after publishing such timetable, the edupage automatically assign last two days as "Saturday and Sunday".

However, if you need to keep the weekends free - so it means, than your sequence goes: 1,2,3,4,5,-,-,6,7,1,2,3,-,-, ... and so on, then all you need is to add the change for the first day of the school - "Day1". Then edupage understands, that you work in cycles and assign all following days with free weekends. The advantage is, that even, if the school year doesn't start on Monday all you need is still this one change.
See the following picture:

See also:
How to set exact date to change the week or the term in published timetable