I have no idea where I've gone wrong. Given the following
cells:

J13= Start Date & Time
K13=End Date & Time
AE66:AE83=Range of non-working holidays
H5= Start of workday (a time)
H6=End of workday (also a time)

I've evolved (with a lot of help) the followng formula.
It is supposed to return the number of workdays and
workhours between the start date and time and the end
date and time. Much of the time it works pretty well, but
too often I'm getting negative hour counts. I have no
idea where I've gone wrong. HELP! I'm desperate and
tired. Here's the formula:

=IF(AND(INT(J13)=INT(K13),NOT(ISNA(MATCH(INT(J13),
AE66:AE83,0)))),"0 days 0 hours", IF(INT(J13)=INT(K13),
"0 days " & ROUND(24*(K13-J13),2)&"hours",
MAX(NETWORKDAYS(J13+1,K13-1,AE66:AE83),0)+
INT(24*(((K13-INT(K13))-(J13-INT(J13)))+
('H6'-H5))/(24*('H6'-H5)))&
" days "&MOD(ROUND(((24*(K13-INT(K13)))-24*H5)+
(24*'H6'-(24*(J13-INT(J13)))),2),
ROUND((24*('H6'-H5)),2))&" hours "))

Does anyone know how I can rewrite this to make it
consistent? All I need is, for a wide variety of
starting and ending dates/times, to calculate the number
of workdays and workhours between the two.