Kroloteans first appeared in Green Lantern #4 (2005).
This show marks the first appearance of Black Lightning, who has apparently joined the JLA sometime in the 5-year gap between seasons 1 and 2.
This show marks the first appearance (as YJ team members) of Batgirl, Bumblebee, Beast Boy, Mal Duncan, and L'Gann. These characters, or their secret identities were all introduced in the previous season in various non-hero roles. It also marks the first appearance at all of Wonder Girl and Blue Beetle.
Included as a bonus cartoon from the DC Comics Vault on the bluray release of Justice League: War (2014).
The events depicted occur on January 1st, then 5 years later on January 1st, 3rd, 4th, and 5th.