The quest you are referring to would be [AREA] Combat Specimen
and was a 1 time quest. Not really sure why you would want to actually pick that quest up except for the sake of just doing it because the only reward you received from it was 11k credits
. Besides that quest, the 3 world bosses are treated just as world bosses.
Both 8 and 16m share a lockout within the same difficulty just as any operation. This has not changed since the last time they released the event.