gmailAutoarchive.js

function gmailAutoarchive() {
  
  var delayDays = 2; // will only impact emails more than 48h old
  var maxDate = new Date();
  maxDate.setDate(maxDate.getDate()-delayDays); // what was the date at that time?

  // Get all the threads labelled 'autoarchive'
  var label = GmailApp.getUserLabelByName("autoarchive");
  var threads = label.getThreads(0, 400);