having arms parallel isn't right for everyone. i personally sit on the lower end. You have to find what works for you. No matter how many octaves you work in a day if you are working with slow practice and with complete relaxation it shouldn't start to hurt. (unless you are playing at FFF). if pain starts when you speed it up then you are tensing up.
thankfully, we don't have to rest our chin on the piano.
i'm assuming in the end it'll hurt continuously, but can you tell prior to officially stuffing your hand up in some way that you're on the way to injuring yourself?