That sounds a awful lot like what used to happen a few years ago with TabTip.exe (basically a Windows tool for touchscreen) which would consistently make games crash after half an hour... You might want to check that out and disable it if possible. Otherwise there could be other factors at play, like a memory leak (to confirm that, just look at the game's memory use, if it always freezes around the same threshold then that's the limit).

And in any case, you might want to verify the game's files through Steam just to make sure it's not a problem caused by corrupted files.