Google Sheets: calculate working hours

given working hours for each weekday (Say Monday through Friday from 9: 00: 00-17: 00: 00), a Start timestamp (eg 1/15/2019 6:15:15) and end time stamp (eg 1/21/2019 14:35:10) …

How can I get that? Total working hours between beginning and end except all other hours (ie on weekends, 17: 00: 01-8: 59: 59)?

I need a basic, reusable formula that does the following in many cases:

Begin: 15.1.2014 6:15:15
The End: 1/21/2019 14:35:10
Working hours: 41:35:10

Note again that I Not count every hour for every day, just within the working hours For every day.

POWER DAYS Unfortunately, it does not give the exact decimal number.