Change cell color based on time

Question

I have a row with 24 cells. I want each cell (from left to right) to change color based on the time. Each cell will represent 1 hour A1=Midnight, B2=1AM, etc... At those specific hours I'd like the corresponding cell to change color. So, at midnight, A1 will change from white to red. I figured I could do this with conditional formatting.
I created a table with =NOW() and formatted it to display only the hour. I then created my 24 column row and pointed each cell in that row to that =NOW() cell. Each cell now displayed the current hour. I setup conditional formatting so that, for example, if A2=1AM (as displayed in the cell) then the formatting would change, but this didn't seem to work. I'm guessing the conditional formatting is just seeing the formula and not the value in the cell. Any thoughts here?

Answer 1

There are a couple of issues involved:
1. Conditional formatting rules compare the value in the cell to be formatted to a fixed value or to the value in another cell. If the rule says "=", then the values must be exactly the same.
2. Date and Time values in Numbers always contain both a time component and a date component. Always. The cell may be formatted to display only the time, only the date, or both, but no matter what is displayed, the values are equal only if the complete Date and Time value is the same.
3. "Midnight", "1AM", are text values. They will never be equal to a Date and Time value.
So the problems are to:
• Extract the Hour from the Date and Time value returned by NOW()
• Convert that number to a text value in the form "9AM", "9PM", or optionally "Midnight", and I presume, "Noon"
• Store that changeable value where it may be compared to the value in the cell to be conditionally formatted.
• Construct the rule to format the cell(s).
Row 1 contains a sample of the 24 cells to be formatted.
Columns D and E, rows 2 to 25 are a LOOKUP table, where the HOUR value is looked up and the corresponding text value returned.
F2 (highlighted with an orangeish fill) contains the formula which extracts the HOUR value from NOW(), looks it up and returns the value displayed (and to be compared).
F2: =LOOKUP(HOUR(NOW()),D2:D25,E2:E25)
Regards,
Barry
Edit: Second thought
The LOOKUP table can be avoided using this formula in F2
=OFFSET($A$1,0,HOUR(NOW())-15)
The -15 at the end of the formula works for my sample table, in which column 1 (column A) is 3PM. For column A=Midnight, the shift should be -0 (or just left off).
Message was edited by: Barry