I am very new to bitcoin mining and am unsure if I set up GUIMiner correctly. I have a new MacBook Pro with a discrete graphics card (ATI Radeon R9 M370X) and am getting about 129 Mhash/s according to GUIMiner. However, it says "Shares: 0 accepted" in the bottom left side of the window. How long does it take for shares to accumulate? Did I set something up wrong? It has been running for about 3.5 hours.