I would like to be able to caculate working time when the cell format is
4/1/2005 6:40:26 AM (not seperated into date and time)

Cell A1 dd/mm/yyyy h:mm:ss (First Day)
Cell A2 dd/mm/yyyy h:mm:ss (Last day)

Working hours would be 8:00 to 17:00
Public holidays need to be taken out too

The result should be working days hours and minutes or just hours and
minutes, so that Saturday, Sunday, public holidays & between the hours of
17:00 to 8:00 to the next working day would not count.

I've tried using:

=((NETWORKDAYS(A1,C1)-2)*9)/24+TIME(17,00,0)-B1+D1-TIME(8,00,0)

But I think this will only work if the date and time are in seperate cells.

Can any one help