Well, it's supposedly all of his research. And you should remember that Ansem was out of the RoD for a good year or so. We know of CoM to the moment in KH2.
So there's another large gap that he had. It's not certain when exactly he put his research into Sora, he could've done it the last day for all we know.
But the main thing, it's Ansem's research. Which I'd presume is all, if not most, of his research, and it consists of the heart (and more). All of which will be key in saving those needed to be saved.
So I'd guess the some of the research on the heart he conducted before he was banished, and then more when he returned.
I don't know what short amount of time you are thinking of. Even if it's just research he conducted in the year Sora was sleeping, that's still a substantial amount of time. Though for science, maybe not.
Thank you for explaining. The second statement bolded was actually what I was originally thinking, BTW.