How do I get this formula:
=SUMPRODUCT(--(D$5:D$31-I$5:I$31<60))

To ignore empty cells? It's currently tallying all the empty ones
contained in the ranges.

Something like this maybe...

=SUMPRODUCT(--(D$5:D$31-I$5:I$31<60)*(D$5:D$31<"")*(I$5:I$31<""))

where you include additional logical expressions to filter those conditions.

Rick