Having gone and poked around in game...
Gamespeed/framerate cap settings go from 1 (marked "slowest") to 7 ("fastest"). Gamespeed 4 is marked "normal", and is where the timer will actually match up to real life. The campaign is (supposed to be) locked to gamespeed 5 ("fast"); that was put in place by Westwood, so it's the same for vanilla RA2/YR as well.
The gamespeed slider is only accessible in skirmish/multiplayer. There are ways to unlock it for campaign, but that's one steaming hot kettle of fish I'm not poking my toes into again.
One thing that I've been wondering about though; if Westwood always intended the game to be played on "fast", then why didn't they make the in game timer match real life on that setting as opposed to on "normal"? All it does is make people panic when/if they realise they haven't budgeted their time correctly because the mismatched timer is throwing them off.