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After scroll down you will see section Non-working days and you can start setting up! For detail information about setting see video below:
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https://www.youtube.com/watch?v=422e2MO2-gk&list=PLGrwYyCxmp1RjVv_gk7TzUZpOnhoOUDot&index=3
It's important to note, that these setting up influence f.e. invoicing or posting.