input date when criteria met?

This requires a "worksheet_change" macro, a sheet-level macro, active all the time on your sheet. The good thing is that you CAN do what you want.

For instance, you could tell the worksheet_change macro to watch for value changes in column A. Whenever one occurs (like starting a new row of data), it automatically puts the date into column B for you. Very nice.

But there is a down-side to worksheet_change macros. They cause your sheet to lose the UNDO stack. So you can never just press Ctrl-Z to undo the last thing you did, there's never an undo-list for that sheet to use.

If that's ok, I can help you with that macro. Tell me what column you want "watched" and what column you want the dates to then appear in. For instance an entry in A2 could trigger a date in B2.

Also, if we're watching column A and on a row that ALREADY has filled out data, someone makes a change in that trigger column, do you want the date that is already in that row to be overwritten with a new, never overwritten, or a popup asking what to do?