Well, I can do an OpenACS install in about 5 minutes now, from checkout from CVS to running server. But I have all the components installed (AOLserver, Postgres on some boxes, Oracle on others, all the required libraries, etc).
So I'm not sure where you might have got the 1 day figure, but I suppose if you had to compile everything from scratch, find all the necessary libraries, etc it could take you a day. Or if you had to install Oracle, it definitely could take you more than one day, especially if you need to apply patchsets and so forth.