Scheduled Posts and wp-cron – Why don’t scheduled posts publish if too old?

Not sure the exact answer but I have a theory that it is a 24 hour window. You can get around relying on wp-cron and someone visiting your site every day by having your server handle your cron. Assuming you have cpanel, it’s fairly easy to do.

Then just have this run every 12 or 24 hours. By disabling wp-cron, you also reduce a little load on your server, as otherwise, wp-cron will ask if it has jobs to do, every single time a page is loaded.