Reverse-engineering an Apparat RTC card for Y2K compliance

The Compaq Portable that I've restored comes with a couple of after-market additions, one of which is an RTC card from Apparat - the rather boringly named "Clock/Calendar Card". Unfortunately, information about this card is quite difficult to come across online, and all I have to work with is the original software, sourced from the original image of the Compaq's hard drive. Oh, and the software isn't Y2K-compliant! The horror! Well, I guess it's time to patch it before the next millennium arrives...