Timing is everything

WE HAVE a 2001 2.2-litre four-cylinder Toyota Camry that has done 47,000km. I know many manufacturers recommend changing the timing belts in their bigger cars at 100,000km and the smaller motors at 60,000km. We bought our Camry new and, on looking through the service manual, I can't see any mention of changing the belt until the 150,000km service, which seems high for a four-cylinder engine.