I'm trying to subtract to sets of dates to figure out the time between but I
need my formula to exclude all weekends and any hours before 8:30AM and after
5:00PM. I have a formula that seems to work most of the time, but gives me an
incorrect result sometimes. Here's what I'm using:

=NETWORKDAYS(a2,b2)-2+((WEEKDAY(a2,2)<6)*(MAX(0,TIME(17,0,0)-MOD(a2,1))))
-((WEEKDAY(a2,2)<6)*(MAX(0,TIME(8,30,0)-MOD(a2,1))))+((WEEKDAY(b2,2)<6)
*(MAX(0,MOD(b2,1)-TIME(8,30,0))))-((WEEKDAY(b2,2)<6)*(MAX(0,MOD(b2,1)
-TIME(17,0,0))))

Here's what it's giving me as an example:
correct result:
Start Time: 1/18/08 4:59 PM
End Time: 1/21/08 8:30 AM
Correct Result: 0:01:00 (HH:MM:SS format, 1/18 is a Fri so there's been only
1 minute of work time elapsing between the two times)

Incorrect result:
Start Time: 1/15/08 4:59 PM
End Time: 1/21/08 8:30 AM
Incorrect Result: 72:01:00 (I should see 25:31:00 for work on 1/16, 1/17,
and 1/18 plus one minute on 1/15.

The formula seems to work in hundreds of rows of my data but misses others.
Anyone know why? Thanks for all the help!

Jon