Hi,
The above formula has since been adjusted and now calculates the hours between 2 dates excluding weekends based on serial hours.
=IF(OR([Start Of Holiday]="",[End Of Holiday]="",[End Of Holiday]<[Start Of Holiday],[End Of Holiday]=[Start Of Holiday]),"",IF(DATEDIF([Start Of Holiday],[End Of Holiday],"d")-(((DATEDIF([Start Of Holiday],[End Of Holiday],"d")+WEEKDAY([Start Of Holiday],3)-WEEKDAY([End Of Holiday],3))/7)*2)+1*(WEEKDAY([Start Of Holiday],3)>5)-(WEEKDAY([End Of Holiday],3)-4)*(WEEKDAY([End Of Holiday],3)>4)<0,0,IF(([End Of Holiday]-TRUNC([End Of Holiday])/1)-([Start Of Holiday]-TRUNC([Start Of Holiday])/1)>0.3,((DATEDIF([Start Of Holiday],[End Of Holiday],"d")-(((DATEDIF([Start Of Holiday],[End Of Holiday],"d")+WEEKDAY([Start Of Holiday],3)-WEEKDAY([End Of Holiday],3))/7)*2)+1*(WEEKDAY([Start Of Holiday],3)>5)-(WEEKDAY([End Of Holiday],3)-4)*(WEEKDAY([End Of Holiday],3)>4))+1),((DATEDIF([Start Of Holiday],[End Of Holiday],"d")-(((DATEDIF([Start Of Holiday],[End Of Holiday],"d")+WEEKDAY([Start Of Holiday],3)-WEEKDAY([End Of Holiday],3))/7)*2)+1*(WEEKDAY([Start Of Holiday],3)>5)-(WEEKDAY([End Of Holiday],3)-4)*(WEEKDAY([End Of Holiday],3)>4))+0.5))))
Basically if its a weekday and the difference in hours is less than 0.3 (serial hours) it will mark as half day. Over 0.3 is a full day
This should work for you also once you have replaced the column names.