I'd assume awhile... lol. I Believe The Sirius sytem (Canius Such-and-such?) is something like a couple quadrillion m away from earth. x10^16. Anyway, that would be just around 8 light years (assuming I have the distance correct), so assuming the sleeper ships were going at the speed of light, you've got around at least 8 years, provided it could start at the speed of light and then stop. So there is your minimum.

The intro on the demo didn't mention it so as for the actual game, I don't know. But if I had to make a scientfic guess, I'd say it would have taken them at least 200 years or more (going about 100 times faster then we can today). So anywhere from 8-200+ years. Maybe someone with more info on the game can give you the real data.

Thanks Prof, i wasnt sure how far away Sirius was, i knew it would be a good walk though ..
i'd assumed they were going at sub light speeds because one of the ships(cant remember which one) got there 20 years after the others...i just cant seem to find any info on exactly how long it took the first one to get there !

I figured it up once based on info I got from the game but I can't remember... I think on average it was ten to twenty years for Liberty to make landfall.