Found this posting on warcry.com regarding NM spawns after maintenances. Not sure how accurate it is, but may be worth researching. Let me know what you think.....

When the servers come down for maintenance they're reset. A server reset spawns all the NMs and HNMs usually, upon coming back up. I did this once with Lizzy, but I usually don't bother, because no matter how hard you try, there's always going to be someone to get the download finished and log on before you, especially on the big NMs - VE, Lizzy, Mysticmaker, etc.

There was a big deal going on over at the Leviathan boards on Killing Ifrit and the general boards at Alla talking about how all HNMs will be in NA prime time now, since the servers are set to come back up around 7pm CST. If the 24-hour spawn HNMs are killed pretty quickly thereafter, they'll continue respawning in NA prime time until the next server maintenance.