Il Trittico is actually three one-act operas in one, all by Puccini. In order, they are:
Il Tabarro (The Cloak, sounds like it's spelled),
Suor Angelica (Sister Angelica, [sister like a nun], sounds like /Soohr/ Angelica), and
Gianni Schicchi (which is a character's name in this opera, sounds like /jee-AHN-nee SKEE-kee/). You can read about the character lists and plot synopses on Google. The tune you'll recognize from this opera is the mega-famous soprano aria "O mio bambino caro" from Schicchi, which you'll see is actually kind of a farcical and manipulative song, not the sweet lovey thing it seems like on all the Opera's Greatest Hits CD's.
I've never done the show, but I do know about it. Trittico is pretty easy as operas go, because it has no dancers or kids, and there is only a small chorus in the first two parts. It is fairly easy on the singers and principal casts are small (for opera!). A director can really show his or her range with Trittico, because Tabarro is very dark and dramatic, Suor is pious and redemptive, and Schicchi is high comedy bordering on slapstick at times. I'll check the run time with SM friends who have done the show, but I think it should be more like 3.5 hours with intermissions (you'll probably take two short ones). The 4 hour time I think comes from a Met video release that also features interviews, etc, on the DVD disc. In fact, maybe you should get the disc, just to familiarize yourself with the operas. You will probably be looking at complete set changes between acts, depending on the flexibility of the design.
If this is your first opera, you'll just need to get used to working with singers and a maestro. Hopefully you'll have a fab SM who will teach you all you need to know. Oh, and always call it a score. Not a script.
Let me know if you have more specific questions about working opera in general or this one in particular. Toi toi toi!