it can be sooner than 30 days after dec 15The Second "acceptance day" can't be sooner than 30 days after December 15th. So roughly around January 14th-January 16th they could probably start accepting more students. No one knows for sure how many spots are filled on initial acceptance day. But like @macsak alluded to above, they have high turnover for their seats. Presumably bc of high costs and being in NYC, and maybe a number of other things. Lets focus on the positives, you got an interview! Now lets see what happens come december/january. You never know.
it's more practical to wait until then, because you would have a better idea how full your class is
but there's nothing to prevent a school that had a ton of cancellations between 12/15 and the end of the year to have a meeting and choose the next round in the beginning of january when school gets back in session...