You have to setup your calender in BP system.
In the system you could set working day & holiday , and if your country's holiday is special , you have to create a Object , which input a date , and could calculate your next working day, i remember there is funtion called ""Is Working Day"" .
Meanwhile , to makesure the Robot could run every month , you have to shedule every month 9,10,11 or even more. Before the real process run , you should desgin a process to help check if it is working day or holiday .
It can be solved , but a little bit complicated.
