If you can make table changes, you can have an ID such as DayOfWeekID. With this column, you can filter you count metric on the DayOfWeekIDs. For example, Monday = 1, Tuesday = 2, Wednesday = 3, etc. Your metric will Count Date where DayOfWeekID Not In (7). 7 being Sunday.
Or, if you are using this metric to divide revenue for a specific time period, then you may be able to count distinct Date from your fact table if your fact tables only have data on business days.