Creating an Artificial downtime for maintenance for only week and work hours

I am trying to calculate downtime within DOMO. The downtime we have currenlty coming from the other system does not put in the factors of weekends and holidays as well as after hours. How can I calculate a correct amount of time between the starttime to endtime while only subtracting within the window. For example if A start time on Friday and an endtime on that next Monday I would not like to account for the hours over the weekend but true business hours. I have tried multiple formulas and getting the same problem. Let me know your thoughts. Thanks