Once the bus starts wind up the mountains and the scenery changes dramatically to lush mountains and beautiful foliage (in autumn) you will soon reach Shima Onsen.
You should arrive a bit after noon. I highly recommend to leave your luggage with your hotel (you won't be able to check in before 3-4pm anyways) and use the time to explore Shima Town. Since this town is so small, most shops close around 4pm so do your souvenir shopping early! Make your way slowly down the hill until you reach the turquoise Shima Potholes. (about 2km down from the bus stop)