Greetings, I am new to the excel forum so please forgive any breach of protocal

I am trying to write a formula to determine the number of working hours and minutes between two dates (orders accepted and orders completed). I only want to consider working hours (6:15-3:15) and exclude weekends and holidays.

Example;
Accepted 9/20/2012 3:36 PM
Completed 9/24/2012 7:07 AM

This order was accepted after the close of business for us so the answer should be 9.867 hours (9 hours for 9/21 and .867 hours for 9/24).

I found a formula from a thread a couple of years ago, but I must be doing something wrong in applying it to my situation
=(17-HOUR(A2)+(MINUTE(A2)/60))+((NETWORKDAYS(A2,B2,"3/7/2011")-2)*8.5) + (HOUR(B2)+(MINUTE(B2)/60) - 8.5)

If some can help it would be much appreciated. I have over 30,000 rows of data to make this calculation for