Theresa,
I don’t think it would take more than a week or two to get the plates composited and a rough cut put together.
The people doing music and foley can’t really do their thing completely until the cut has been tightened up and locked down completely in terms of timing, though – and the people doing titles and credits can’t finish until the very very last stage before final editing polish and mastering.
The big gotcha for the keepers of the schedules on this is rework. It’s inevitable that some pieces will need a little more punch, or in context the lighting or timing will need to be tweaked, etc. Rework will have to be done, and it may have to go all the way back through the animation, lighting and rendering crews again and checked again for consistency before being reinserted into the work print.
Don’t forget rendering time, either. The piece is fairly simple, but at high def res with global illumination, it’ll still take a non-trivial amount of time (we can get a pretty good estimate on rendering time once lighting tests happen). Not to mention that if we’re cranking out a minimum of 15 plates & passes at high def uncompressed resolution to a server, just uploading the renders might take a few days.
We’re still shooting to have a finished product before siggraph, right? In that case, I’d work backwards from July 20 in setting dates for major post milestones and give as much room as you can for rework and polish.