I've finally been able to give  these suckers a try, and I can't
get any of them to work. They all return "#VALUE!". Let me give you some
more specifics that may help:

The columns  of dates  and flows are not next to each other. Dates are in
column AC, and flows are in column AG. Also, the dates are actually times.
They are in increments of 15 minutes, over several days (it's a large
spreadsheet).

The UDF returns a value, but not the correct one. Do you think these formulas
can still work?