During Superman's speech, all the existing JLA members are lined up on his right according to their presumed transporter code numbers, except Captain Marvel (15) and Red Tornado (16) who have swapped places at the end of the line. To this point in the series, numbers have not been heard for Wonder Woman, the Green Lanterns, the Hawks, or Captain Atom. There are only 15 members on the podium because Zatara (11) is also present as Dr. Fate. Given the order of presentation of the newly-inducted members, it can be presumed Dr. Fate will be #17, Plastic Man will be #19, and Red Arrow will be #21. Atom's card has "18" printed on it, and Icon is given #20 as he and Canary beam up.
Appearances of Arc #16: two of the microphones in front of Superman are from Channel 11 and Channel 5; 11 + 5 = 16. The third mic is from Channel 7 "Sixteen" has 7 letters. Also, as of the beginning of these events, there have been 16 officially recognized members of the JLA.
The events depicted occur on December 30th.