Brendan Moody wrote:
Filming started April 2nd, the day after the read-through, so it's more like four weeks than three. But four weeks is the usual shooting time for a 60-minute special; if they'd been working from a 90-minute script it would have taken more like six weeks. So certainly closer to 60 than 90, as Allyn says.
And shooting in 3D will have slowed things down a bit too.