Subtract two times, exclude weekends

My proposition:
=NETWORKDAYS.INTL(MAX(A6,WORKDAY.INTL(A6-1,1,1)),B6,1)-MOD(MAX(A6,WORKDAY.INTL(A6-1,1,1)),1)+MOD(B6,1)

And format for instance as [hh]:mm
Please note that in last row you will get negative number, because as opposite to " I do not want Saturday and Sunday ..." the arrival is on Sat and processed on Sunday :-(

Using NETWORKDAYS.INTL is a good idea because it allows to easily take into account holidays.

if you want to have it as a number of hours take
=(the formula_above)*24
and use general format