Look for ISS viewing opportunities during the first and last two days of the Atlantis mission, since Atlantis will be chasing after the ISS during these periods. So if you see viewing opportunities on 14-16 May, then watch for Atlantis to follow essentially the same path as the ISS a few minutes after you see ISS. As the time for docking approaches on 16 May, the distance between the craft will diminish.
Atlantis will not be quite as bright as the International Space Station, but it is easily visible. Good hunting!