My estimate: one day for web/db programmers. Maybe a long weekend weekend for a programmer with a UNIX background. This is assuming that you've actually read the various installation guides and manuals, you're a conscientious, detail-oriented person, and you're not trying to do this at 3 a.m. when you're dead tired.
My background: I am an erstwhile technical marketing guy; I was briefly a web/db programmer. My educational background is liberal arts. I've been on UNIX/Linux boxes for about eight years. I've been involved with the ACS/OpenACS for about three years. I'm not really a programmer; I used to be an okay sysadmin many moons ago.
From what I've seen in both the ArsDigita bboards and this OpenACS one, people with limited UNIX experience will need to allocate more time to learn some of the *nix nuts and bolts. There are some "Learn Linux in 21 Days", but that will take you, uh, 21 days, I suppose.
Also, from what I've seen, the vast majority of problems seem to related to A.) botched editing of the nsd.tcl configuration file, B.) botched editing of the ad.ini configuration file (or whatever it's called), C.) incorrect/botched TCP/IP network configuration, and D.) not paying close enough attention to the documentation. The first two mistakes are often explained later as "Uh, I was really tired when I was doing this". The third mistake is usually a *NIX newbie mistake. The fourth mistake cannot be attributed to any particular reason other than some people have better reading comprehension than others.
Thankfully, you do not have to install Oracle, another big can of worms that could add days and/or weeks to your installation.
