When they first came out with the white engines the interval was 60K but I think they eventually went away from that. We never really changed them as a routine 60K item at the dealership. Reason being was some of the cars had them changed already and did not need it, some of them were running the original and still did not need it, and all of that stuff was going to be coming apart in 10K for the 70K belt change. So the answer to your question is to monitor that belt as part of routine service and change it out when it needs it. A word of warning though, I have seen more than one of those belts come apart, get into the timing belt area, and cause the T-belt to snap and destroy the motor. So while those serp belts will go a long long way even when it sorry ass shape do not push it too far or you may regret it big time.

Mark