The Google Script will automatically archive all the messages in your Gmail inbox that are older than 2 days. You can either use a Gmail search filter to find read messages or you can compare the message date with the current date through the script and archive messages accordingly.
function cleanInbox() { var delayDays = 2; var maxDate = new Date(); maxDate.setDate(maxDate.getDate()-delayDays); var threads = GmailApp.getInboxThreads(); for (var i = 0; i < threads.length; i++) { if (threads[i].getLastMessageDate()