Tracking elapsed business hours

I'm looking for a function that will track elapsed business hours only. So, it should exclude non-business hours, holidays, and weekends. I've tried the function below, but it fails if the start date/time or end date/time fall outside of business hours. Even though I don't want to track non-business hours, I do have to be able to log them.

=ROUND(IF(NETWORKDAYS(A1,B1,luHolidays)=1,(MIN(luDayEnd,MOD(B1,1))-MAX(luDayStart,MOD(A1,1))),(NETWORKDAYS(A1,B1,luHolidays)-2)*(600/1440)+(luDayEnd-MAX(MOD(A1,1),luDayStart))+MIN(MOD(B1,1),luDayEnd)-luDayStart)*24,0)/24

A1 contains the logged start date and time (e.g. 2006.01.22 7:00 AM)
B1 contains the logged end date and time (e.g. 2006.01.23 10:00 AM)
luHolidays contains the list of holidays
luDayStart contains the beginning of the business day (e.g. 8:00 AM)
luDayEnd contains the end of the business day (e.g. 5:00 PM)

Can any of you experts help me?

Try this,

=(NETWORKDAYS(A1,B1, luHolidays)-1)*(luDayEnd-luDayStart)+IF(NETWORKDAYS(B1,B1,luHolidays),MEDIAN(MOD(B1,1),luDayEnd, luDayStart), luDayEnd)-MEDIAN(NETWORKDAYS(A1,A1, luHolidays)*MOD(A1,1), luDayEnd, luDayStart)

format result cell as [h]:mm

The formula works perfectly. Thank you.