Abstract: An apparatus, as well as a method, brings a surface of a substrate into contact with a polishing pad. A light beam is directed by an optical endpoint detection system to impinge the surface of the substrate. A signal from the optical endpoint detection system is monitored, and if a first endpoint criterion is not detected within a first time window, polishing is stopped at a default polishing time. If the first endpoint criterion is detected within the first time window, the signal is monitored for the second endpoint criterion, and polishing stops if the second endpoint criterion is detected.