Although it is difficult to overcook pulled pork, it can become too soft if cooked for too long past the recommended cook time. Pulled pork is ready to enjoy after a little under 5 hours on High heat in the slow cooker; however, as long as you don't shred it until you serve it, you can safely leave it cooking overnight on Low heat. If you cook on Low overnight, I recommend leaving it to cook in the slow cooker for about 10 hours.