I'm having an issue trying to get this formula to work. I have a due date
which is when documents are supposed to be turned in and then their actual
dates - when the docs were actually turned in.

I need to know the difference between these two dates and if the difference
is greater than zero (meaning they turned it in prior to the due date or it
still hasn't been turned in - the cell is blank), the average of those
differences.

The current formula I'm using is:
=AVERAGE(IF((O12-O9)0,(O12-O9)),IF((O14-O9)0,(O14-O9)),IF((O16-O9)0,(O16-O9)),IF((O18-O9)0,(O18-O9)),IF((O20-O9)0,(O20-O9)))

It returns the average of all difference in dates, including the zeros. I
tried making it an array formula like the following one, so the zeros could
actually be null and then they wouldn't be averaged but that doesn't work
either:

{=AVERAGE(IF((N12-N9)0,(N12-N9),""),IF((N14-N9)0,(N14-N9),""),IF((N16-N9)0,(N16-N9),""),IF((N18-N9)0,(N18-N9),""),IF((N20-N9)0,(N20-N9),""))}

Could someone please help me out with this, I'd greatly appreciate it

=)