Spreadheet 1 "Hourly" is referring to Spreadsheet 2 "Daily".

Spreadsheet 1 will contain 744 hourly values in a continuous column.
Spreadsheet 2 has the required data arranged by days with twelve rows
between each successive day's set of 24 hour data.

How do I easily capture the easily refer to the data on Spreadsheet which on
Day 1 is in cells B13:B36, on Day 2 is in cells B49:B62, on Day 3 is in cells
B73:B106, etc.?

There's a pattern, but Excel's not picking it up correctly when I copy the
formulas.