Jagex isn't smart enough to check how long you have been online. I have a 40 hour proggy right now, and that is just because I restarted my proggy after 16 hours, with like a 30 min log out time in between. So 56 hours and counting. It's literally impossible to ban because of all the different stuff you have to do in order to complete a dungeon. It's perfectly safe. If you need some proof, talk to Unspoken. He has days long proggys, and he is not banned.