If they were staggering release by world I wouldn't have seen almost all the worlds on my data center represented when I did it earlier. From what's been reported it looks like all of NA was running from 9pm to midnight PDT.
They don't have to allocate an extraordinary amount of space for it. One instance holding 144 players should require less server space then 36 instances holding 4 players each since it's only 1 set of art and NPC assets being loaded instead of 36.
The problem with having narrow windows restricting when all players can queue is that you end up forcing all players to queue for it at the same time if they want to participate instead of spreading it out over the entire day.
This isn't necessarily going to die out fast like other seasonal events usually do. As a level 68 WHM scaled to 50, I was getting 36.8K XP per FATE. I just went to CWH and did a level 50 standard NM FATE also as 68 WHM scaled to 50 and got 32.4k XP. For someone who's leveling alts jobs in the 30-50 range (and possibly even to 60), this makes a nice change of pace from the normal leveling grind. You might miss out on GC seals (at least I don't remember getting any) but not everyone cares about those.
