If it is the V6, the recommended mileage is 60,000.

I do know a mechanic who works on those 2.7L V6 engines a lot.  He has
hardly ever seen a single timing belt on that engine fail, regardless of
mileage.

But the one or two that did, were caused at least in part by failing spark
plugs.  So even if you are past 60,000, I would never go past 90,000.  And
when you replace the timing belt, have the platinum plugs, as well as the
external belts (which should be common sense) replaced as well.

Now that is ONLY if it is the 2.7L V6.  If you actually have the 4, do not
go one mile over the recommended maintenance interval.  I guess the belt
failure fate on those Optima 4's are much higher.  Thankfully, since '06,
the new Optima 4 has a timing chain instead of a belt.  The V6 is still the
same engine, and with a belt.

Hope this helps.