Life moves at many different paces.  On different worlds, with different biochemistries, some scientists believe the rise of a sapient species will naturally take different amounts of time.  But are they generalizing too much?

BathyGaian & ChloriticGaian (possibly) environments: 3 billion years
EuGaian environments: 4 billion years
Brammian & BathyAmunian: 5 billion years
EuAmunian: 6 billion years
Titanian: 7 billion years

These are based on the expected metabolisms of organisms in such environments, going with the assumption that the evolutionary rate would be somehow proportional to this.  BathyGaian and ChloriticGaian worlds could in theory develop intelligent life faster as BathyGaian organisms would have higher metabolisms from the higher temperatures, while ChloriticGaian organisms would have a dual energy source allowing fasted metabolisms.  Brammian and BathyAmunian environments would be dominated by anaerobic systems and therefore have slower metabolisms than EuGaian worlds.  The arrangement of the others should be fairly obvious and straightforward.