I am using the formula below to calculate the elapsed time between a start time and end time with the working hours of 6:30am - 3:30pm and it will rule out weekend days (Saturday/Sunday).
=IF(T2="","",(NETWORKDAYS(S2,T2,)-1)*("15:30"-"6:30")+MOD(T2,1)-MOD(S2,1))
S2 = start time, T2 = end...