Time Entry Formula

I'm creating a spreadsheet where a test note taker needs to repeatedly enter the date/time code in a column as events occur.

I tried recording a macro that will enter the =now() formula and then copy that over itself with the value but didn't work.

So now I'm thinking I need to just write code that will determine "now", and write that serial value to the next open cell (with care not to overwrite the previous data point). I'd like to execute this with a simple keystroke.

The thought is to start at the top of the column, go down until the next blank cell is reached, insert the time code (can't be a formula that will change but an actual value).