Pabbly Connect Webhook add-on for Google Sheets

I understand that when triggering from Google Sheet by adding data from an external source I should set "Auto Send on Schedule". Is the trigger fired once on the hour and if no change (no rows added for instance) no further trigger?

Yes, the trigger(pabbly google sheet addon) will send all new rows or updated rows(you need to update trigger column cell's value) once per hour to your webhook.