Yes, that timescale is about right. I applied to NAC at the beginning of December and received the I-20 about 10 days later. I thought I’d be really organized and get all the visa forms in advance, so I was just waiting on the I-20 – until I discovered my passport had gone AWOL.
New passport issued 30th December, and 1st available interview at the embassy was the 14th of Jan. As CZ says, the only hassle with the appointment is the hanging around for nearly 2 hours, waiting to be seen. The interview itself was very brief, and they confirmed there and then I would get the visa – it duly turned up a couple of days later.
All fairly painless.