As an example, to add the 25.12.2018 as a closed day each year, the librarian has to activate the "Repeat" button and chose "Yearly" and then the value "1".
It's seems a bit confusing. The librarian can expect that the number "1" means the number of years the rule applies.
The display should be clearer. For example :
Repeat every [number] day(s)/week(s)/month(s)/year(s)