DOOD! Run to the store and buy at least a cheap Haynes manual on Grand Cherokees and read
There is no timing belt at all....
That engine has a timing chain, not a belt, and there is no maintenance or replacement schedule on a timing chain. Maybe someday when the engine is well over 100,000 miles AND IF the engine gradually begins to run roughly or poorly, then perhaps the timing chain may be stretched and causing that. But at that time you'd go through some steps to determine what the problem is, since it could be injectors, throttle position sensor, O2 sensor, etc.
It's pretty easy to determine how much slack there is in the timing chain so it's easy to diagnose. And it's more likely to be an issue at closer to 200,000 miles if you're treating the vehicle right.
I would definitely recommend that you keep a little savings aside in case of a problem. You can assume
that the air conditioner evaporator core will spring a leak very soon if it hasn't already been replaced. And you can assume that will be about a $1000 repair, so keep some money ready for unexpected repairs just in case.
Don't say I didn't warn ya....