SCHEDULED MAINTENANCE UNDER SEVERE USAGE CONDITIONS PAGE 00-47. #7~~ Timing belt Change Every 48 months or every 96,000 km (60,000 miles) So if you baby your engine and rarely hit WOT, you're okay to 105,000. If you are doing pulls all the time, you might want to stick to 60,000 miles.
Here is a video guide on how to remove and replace the serpentine belt and tensioner on a 2006 Mitsubishi Outlander. This procedure should be similar for all PPX10i.