Explore New Metric: Tickets/Business Day/Assignee

Hey everybody,

as the title already says, I want to create a metric that is dynamic and tracks how many new tickets were done per assignee during the variable time frame.

The filters I'm using are "Ticket Created - Date" and "Ticket Groups", which lets me filter by country for our company. 

So if I filter by "Last month" and "Germany CS" I'd like to get the value of new tickets my assignees had to do per business day.

In my head, it should look like this:
COUNT(Tickets)/COUNT(business days)/COUNT(Assignees)

COUNT(Tickets) = tickets created during the variable time frame
COUNT(business days) = amount of business days during the variable time frame 
COUNT(Assignees) = amount of assignees in the team during the variable time frame 

but the attribute "COUNT(business days)" does not exist and I'm not sure how to create it.

The best I came up with is a non-dynamic solution for a week and a month: 
Weekly
VALUE(Tickets created - Daily average)*7/5/COUNT(Assignees)

Monthly
COUNT(Tickets)/21/COUNT(Assignees)

Any ideas how to create a dynamic solution?