It's difficult to use NETWORKDAYS because that won't count Saturdays.
If you have start time/date in A2 and end time/date in B2.....and holiday dates listed in H1:H10 then this formula will total all the working hours between those 2, given MF hours of 07:00 until 16:00 and Saturday hours of 08:00 until 12:00
=(SUMPRODUCT(INT((WEEKDAY(A2-{2,3,4,5,6,7})+INT(B2)-INT(A2))/7),{9,9,9,9,9,4})-SUMPRODUCT((H$1:H$10>A2)*(H$1:H$10< B2),LOOKUP(WEEKDAY(H$1:H$10),{1,7},{9,4}))+(MOD(B2,1)-MOD(A2,1))*24+IF(WEEKDAY(A2)=7,8,7)-IF(WEEKDAY(B2)=7,12,16))/24
<?XML:NAMESPACE PREFIX = B2),LOOKUP(WEEKDAY(H$1 /><B2),LOOKUP(WEEKDAY(H$1:H$10),{1,7},{9,4}))+(MOD(B2,1)-MOD(A2,1))*24+IF(WEEKDAY(A2)=7,8,7)-IF(WEEKDAY(B2)=7,12,16)) p 24<>
format result cell as [h]:mm
If you want to make it more generic then you could set up a table which lists respective start/end times for Sunday to Saturday and then reference that....so if W2:W8 contains the numbers 1 to 7, X2:X8 shows start times Sun to Sat, Y2:Y8 shows the end times (if it's a non working day then start and end should be blank or zero) and Z2 has the formula
=Y2-X2
copied down to show the daily hours.....then the formula would become
=SUMPRODUCT(INT((WEEKDAY(A2-W$2:W$8)+INT(B2)-INT(A2))/7),Z$2:Z$8)-SUMPRODUCT((H$1:H$10>A2)*(H$1:H$10< B2),LOOKUP(WEEKDAY(H$1:H$10),W$2:Z$8))+MOD(B2,1)-MOD(A2,1)+LOOKUP(WEEKDAY(A2),W$2:X$8)-LOOKUP(WEEKDAY(B2),W$2:Y$8)
</B2),LOOKUP(WEEKDAY(H$1:H$10),{1,7},{9,4}))+(MOD(B2,1)-MOD(A2,1))*24+IF(WEEKDAY(A2)=7,8,7)-IF(WEEKDAY(B2)=7,12,16))>