Hi
try this formula
it counts (I think!) the number of working hours between 2 dates, assuming a 12-hour working day (6am to 6pm) Monday to Friday

=12*NETWORKDAYS(ROUNDUP(A1,0),ROUNDDOWN(B1,0)-1)+24*(IF(WEEKDAY(A1,2)<6,IF(MOD(A1,1)<0.25,0.5,IF(MOD(A1,1)<0.75,0.75-MOD(A1,1),0)),0)+IF(WEEKDAY(B1,2)<6,IF(MOD(B1,1)<0.25,0,IF(MOD(B1,1)<0.75,MOD(B1,1)-0.25,0.5)),0))