I created a minimal sheet to demonstrate the problem: https://docs.google.com/spreadsheets/d/1cc8UdkOvIPf_wDGCHaDN0BqR3sX3Teb1qKlvdM1cL3g/edit?usp=sharing
Cell A1 specifies a startDate
Cell A2 displays an endDate.
Cells B4:H8 lists the days of 5 consecutive weeks starting with monday.
Cells A4:H4 compute mondays's date from the startDate.
Cells B4:H8 display the result of the following formula:
=AND($A4 + COLUMN(B4) - 2 >= startDate, $A4 + COLUMN(B4) - 2 < endDate)
As you can see in B4:H8, this formula provides the correct result: true for all dates between startDate inclusive and endDate exclusive.
I can't figure out why this formula does not work to apply conditional formatting...