How to to get coordinates from addresses coming in from importrange?

I have addresses coming in from importrange and I am using this script to get coordinates.

function myFunction() {var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Geo 4')var range = sheet.getDataRange();var cells = range.getValues();var latitudes = [];var longitudes = [];for (var i = 0; i < cells.length; i++) {var address = cells[i][11];if (address == "") {latitudes.push([""]);longitudes.push([""]);} else {var geocoder = Maps.newGeocoder().geocode(address);  var res = geocoder.results[0];if(res){latitudes.push([res.geometry.location.lat]);longitudes.push([res.geometry.location.lng]);}else{latitudes.push([0]);longitudes.push([0]);}}sheet.getRange('O1').offset(0, 0, latitudes.length).setValues(latitudes)sheet.getRange('P1').offset(0, 0, latitudes.length).setValues(longitudes);}}  

The issue is that I have this running on a trigger every 6 hours but I need something that would get coordinates as soon as one address changes without running the whole column and using the 1000 geocodes you get per day. I have about 350 addresses constantly but maybe three change a day.