You will need:
1 encoder, with a fast Internet connection (or better yet, a server dedicated to encoding)
1 or more translators
1 timer (the person who synchronizes the subtitles with the video)
2-3 editors / QCers
1 typesetter (the person that places/styles signs correctly, and stuff like that)
Some kind of collaborative editing system, there are a couple of good ones
Plenty of motivation
Step 0. Encoder downloads the raw, and creates a workraw. A workraw is a raw that's had commercials cut in the same way they'll be cut in the final release, and is usually encoded at a low bitrate. With some raws, such as TV-Japan raws, this can be omitted since the raw is already cut pretty well. (30 minutes)
Step 1: Everybody downloads the workraw. (5-15 minutes, depending on connection speeds)
Step 2: Translation (30 minutes or so)
Step 3: Timing (30-45 minutes, depending on the timer)
Step 4: Editing / QC / Typesetting - These three jobs are traditionally separated, but they're similar enough that they can be combined into one step if you're in a hurry. The fastest thing is for all the editors and QCers to work on the script collaboratively, since at this point there should be no more structural changes to the script. Meanwhile, the typesetter can do their thing, and merge in the changed lines. (1 hour)
Step 5: Final encode - During all this, the encoder should have been doing the final encode(s?), and they should be uploaded by this point. (2 hours)
Step 6: Mux - With softsubs, the finished script can be added to the video in a few seconds, from the command line.
Step 7: Party :3
Pipelining: You can often get some not-insignificant speedups by splitting the episode into chunks of a few minutes, and doing those individually.
The main problem with this method is the difficulty of getting everybody together in one place at the same time, which is probably why it doesn't happen. In the group I'm in we tried it once, and despite the usual problems associated with trying anything for the first time, we managed to sub an episode of Naruto from start to finish in about three hours.