calculate total hours between date/time (excluding weekends)

NeilKloster  so in order to account for every contingency the formula is large but hopefully understandable:

= LET(StartDay, C7, EndDay, D7, DayStart, TIME(7,0,0), DayEnd, TIME(23,0,0),
           incStart,NETWORKDAYS(StartDay, StartDay),
           incEnd,NETWORKDAYS(EndDay,EndDay),
           daysInBetween, NETWORKDAYS(StartDay,EndDay) - incStart - incEnd,
           hoursInBetween, daysInBetween*(DayEnd - DayStart),
           startHours, incStart*MAX(DayEnd - MAX(DayStart,MOD(StartDay,1)),0),
           endHours, incEnd*MAX(MIN(DayEnd,MOD(EndDay,1))-DayStart,0),
           IF(daysInBetween>=0,
                startHours + hoursInBetween + endHours,
                if(StartDay<EndDay, MIN(DayEnd,MOD(EndDay,1))-MAX(DayStart,MOD(StartDay,1)),0)))

so row 1 is the only thing you need to enter with the start day & end day, and then DayStart and DayEnd are the start and end of the work hours.  After that:

lines 2&3: the incStart & incEnd check if the start/end days are weekdays or weekends,

line 4: daysInBetween finds how many valid workdays NOT counting the 1st or last,

line 5: converts full days to # of work hours,

line 6&7: calculate the # hours on the 1st and last days

line 8: checks if # daysInBetween is valid (i.e. Start Day is > End Day)

line 9: adds hours together in 'normal' cases

line 10: calculates # hours if start Day is same as end Day or gives 0 if start is AFTER end