how to calculate between times

hello all

can someone pls advice.
i need to calculate the time between start to finish dates.
A1
08/07/05 12:00

A2
09/07/05 1200

i found this formula =text(a2-a1,"h:mm") to be helpful.
but i want to calculate business hours only which is from 9am to 5:30.
can someone pls advice what formula i can use?
thanks

Try this

=17.5/24-(A1-ROUNDDOWN(A1,0)) gives number of hours worked on 1st day

=NETWORKDAYS(A1,A2) gives number of full (8 1/2 hour) working days (multiply by 8.5/24 to get hours)

=A2-(ROUNDDOWN(A2,0)+0.375) gives number of hours worked on the final day

add them all up and you should have the number of days/ hours worked