I mean I'm new to Metal Gear and all but it is inconceivable that I spent 90 hours on MGS1 so far! I mean some Bosses are tough to beat but all I played was a few hours on some weekends and an hour or two occasionally on a weekday, the game shouldn't take 12 hours so where do these 90 hours come from?
I don't use the gog launcher, but maybe it'll update the play time when you go online? I know Steam can be a bit funny with the play time if you play whilst offline, but it fixes it when you reconnect.
That's very possible I leave GOG on usually, I will check again tomorrow if the hours climbed up significantly