sheets-app-Extension-onEdit-timestamp.js

function onEdit(e) {
    const now = new Date();
    const utcNow = new Date(Date.UTC(
      now.getUTCFullYear(), 
      now.getUTCMonth(), 
      now.getUTCDate(), 
      now.getUTCHours(), 
      now.getUTCMinutes(), 
      now.getUTCSeconds(), 
      now.getUTCMilliseconds()
    ));

    var sh = e.source.getActiveSheet();

    if (sh.getName() == 'Sheet1' && e.range.getColumn() == 1 && e.range.getRow() != 1) {
      sh.getRange(e.range.rowStart, 2).setValue(utcNow)
    }

    if (sh.getName() == 'Sheet1' && e.range.getColumn() == 3 && e.range.getRow() != 1) {
      sh.getRange(e.range.rowStart, 4).setValue(utcNow)
    }
}