Poorly designed instances? Last i did some raids i must admit that i found the zones nicely designed, good challenges.
Im sure that once you got all tactics under your skin and know the zone 100% you can do EH on less than 1 night. And i really dont think SoE meant for people to "save a zone" by simply keeping it open overnight, thats a invention of the players themselves (like snare kiting in EQLive)
Edit: Also, dunno what server your on, but all servers have a specific time that they go down for a resetting/updates - and on EU servers its 4/5 am GMT (5/6 CET) - dont remember time on US servers.