I guess you could say that lots of Genesis and SNES OST's are timeless by virtue of the fact that they sound like Michael Jackson and Paula Abdul songs, which still get radio play to this day.
It's really hard to pick something out as being "timeless", though, because pre-20th century classical music is clearly composed with very rigid and antiquated sensibilities unlike recent compositions, video game music is dated by their sound chips and processors, New Jack Swing was a fad, and most music you listen to can be neatly compartmentalized into belonging to certain decades (I've heard Fred Durnst call Nivana's "Smells Like Teen Spirit" 'timeless' but it definitely sounds like one of those hangover soundtracks that went out of style after the 90's).
What I would call 'timeless' would be the Pixies. I could easily mistake their music for being from the 2000's if I wasn't sure they made their best albums in the late 80's (and I'm counting 1990 and 1991 as 80's as well because the Soviet Union wouldn't collapse until December of '91). So, I think it would be very hard to find something truly timeless from a video game.