I sent a mail to niconico support and here is the reply:

Hello, this is Niconico Customer Support.

Thank you for your inquiry.

Regarding your Moogle attire code,
if you purchased the premium stream by December 21st
you will receive it five days after the event (around the 26th).

If you purchased the tickets via timeshift, you will receive it in a week
or sometime after. Reason being, is that the codes will be sent out in a
batch once every week.
so that mean...it can take longer for some unlucky ppl. I don't remember which option I bought the ticket, but today is the 27th and I have not receive the code