Not sure how well the search function works here but there are lot of posts (and opinions) about your topic. The owners manual for my '99 says 60K but in small print indicates that those of us who live in CA apparently have the "magic" belts that go to 100K. Just kidding but obviously CA and other states have forced Mitsu to at least put in writing that the belts can go 100K. CA dealers conveniently don't seem to mention this too often.
There has to be some safety margin even above 100K (90K in your case) but this is where you'll get all kinds of opinions. There was a recent post of a sad case where the water pump seized at less than 100K and this destroyed the belt (and several valves) so you never know.
My 2nd belt just hit 100K and I'm planning on changing (along with the water pump) very soon.
2005 Montero Limited, Sudan Beige Metallic - 77K Miles (Photo Coming Soon)
1999 Montero, Anchorage Gray Metallic -(Sold @ 227K Miles)