Google-sheets – Repeat last action in Google Spreadsheets

Yes, populating an external service should be possible in a few different ways, all involving Google Apps Scripts:

1. By using the JDBC service to populate an external database directly
2. By using the URLFetch service to call an external web service
3. By pulling data from the spreadsheet from an external app

In any case, you would need to set up a trigger script that will run when a response is submitted to your spreadsheet.

Option 1 might be out of the question if your database is behind a firewall. If you're not keen on doing a lot of Google Apps scripting, a good compromise could be to have a small trigger script ping an external web service to notify it of the new data. The external service would then poll the Google Spreadsheet for data, using for example the XML API.

You say it's just a thought experiment for now (too bad - it sounds like a fun project), but in any case I would really recommend reading up on Google Apps Script. It is a fairly new feature in Google Docs/Drive, and really makes it possible to create quite powerful webapps.

You can try adding a Google Apps Script to capture when a cell is edited and add a timestamp to a different cell. Here's a previous answer that is similar: Google Spreadsheet Timestamp?

function onEdit() {
 var s = SpreadsheetApp.getActiveSheet();
 if( s.getName() == "Sheet1" ) { //checks that we're on the correct sheet
   var r = s.getActiveCell();
   if( r.getColumn() == 13 ) { //checks the column
     var nextCell = r.offset(0, 1);
     if( nextCell.getValue() === '' ) //is empty?
       var time = new Date();
       time = Utilities.formatDate(time, "GMT", "HH:mm:ss");
       nextCell.setValue(time);
   };
 };
}