calculate total hours between date/time (excluding weekends)

I think this is same as another question:
https://techcommunity.microsoft.com/t5/excel/networkdays-formula/m-p/3693884
here is my answer there:
= NETWORKDAYS(C2,D2) - 1 + MOD(D2,1) - MOD(C2,1)
and format cells as [h]:mm:ss as you noted.
but again this doesn't take into account any work hours and doesn't account for any start or end dates that are on the weekend.
If the start or end might be a weekend then try:
= NETWORKDAYS(C2,D2) - NETWORKDAYS(C2,C2) - NETWORKDAYS(D2,D2) + 1 + MOD(D2,1) - MOD(C2,1)

EDIT after thinking about this if it starts or end on a weekend then the MOD parts (the hours) shouldn't count either so:

= NETWORKDAYS(C2,D2) - NETWORKDAYS(C2,C2)*(1+MOD(C2,1)) - NETWORKDAYS(D2,D2)*(1- MOD(D2,1) ) + 1

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