Mac Numbers date functions

This currently isn't possible. Conditional highlighting will only run the condition on the cell that the rule has been applied to.

To change the appearance of a cell based on its cell value, create a conditional highlighting rule.

^{Source: Add conditional highlighting to cells — Numbers Help for Mac; emphasis mine.}

The only exception to this is for conditions where a comparison is required — a second value can be referenced in the rule.

Click to use a cell reference. A cell reference lets you compare the cell’s value to another cell—so, for example, you can highlight a cell when its value is greater than another cell’s. Click a cell to select it, or enter its table address (for example, F1).

^{Source: Add conditional highlighting to cells — Numbers Help for Mac.}

As a workaround, you could duplicate (or reference) the column A and place it next to column D, applying the conditional highlighting to that column instead. It won't be highlighting the cell with the data, but it'll give you something to glance at next to the data.

I believe Insert > Date & Time (and its two companions) are intended for use in headers and footers. These are available after choosing File > Print. When used there, the inserted date can be clicked for a little popup formatter and button to manually reset the time to now.

The feature you want, an auto-generated NOW cell that does not change, is apparently not available.

Option A: Put the NOW function into a cell somewhere. It shows the current time. Copy the cell, then Edit > Paste Formula Results into the cell you want to have the unchanging time.

Option B: Use a general macro app (like the amazingly capable Keyboard Maestro) to generate your date/time text and paste it into a cell.

In both cases, choose the date and time formats you want on the final cell.

(Numbers 3.5.3 used for this answer)