When I say "time centered reward", I mean that no matter what you do or how you play, only time will decide when you get your reward.
In fact, missions are never "time centered". The only thing required to progess is the skill to win the mission. Imagine you're doing "United We Stand" and you only randomly gain access to "To Kill a Raven" ? Pretty stupid, isn't it ?
Soboro, Swift Belt and such are only drops from several NM. It's not so different from the rest of the Rare/Ex items (with ridiculous drop rate).
