I don't think the discipline of computer user interfaces has been around long enough to say anything is "timeless".
I am sure people making advertising art in the 1950s thought their work was "timeless" too but from a modern perspective there sure is a distinct look; today's Apple-led "minimalism" will probably look just as archaic most of a lifetime later.
IIRC apple were the last to get off the skeumorphism train. Microsoft's metro look was the first significant player in this round of the minimalist trend
I am sure people making advertising art in the 1950s thought their work was "timeless" too but from a modern perspective there sure is a distinct look; today's Apple-led "minimalism" will probably look just as archaic most of a lifetime later.