estimated nm spawn time websiteFollow

I don't know if there's really a spawn time limit. I come to this conclusion after watching my roommate hunt the NM "Ashmaker Gotblut". Ashmaker spawns in a small room of the grotto's. At first my roommate would just sit there and wait hours for the Ashmaker to spawn. Finally after a few times of killing it, he got bored of waiting and killed the other spawns. It is both of our beliefs that killing a certain type of mob raises the chance of the NM spawning in the next spawn.

EX) Hunting the Jaggedy-Earred Jack in H-9 of w. ronfaure. I go around and kill all the rabbits I can find and generally spawns him sometime between dusk and dawn of that same night. If I just run around and look for him without killing anything, I may run around for 3 game days.

oh also, I think I may have figured out the best luck for getting that exclusively rare drop (like the rabbit charm from the jaggedy earred jack). I'll continue using Jaggedy as an example as I have fought him several times. Note the crystal that COULD be dropped after defeating the NM and try to hunt the NM on the day corresponding to the crystal while the moon is full. I think that would give you the best of luck... my roommate got the priest's robe under the conditions of Firesday on a 94% full moon.

The theory you just described above is one that has been around for quite a while. In Everquest, we said named mobs (the equivalant to NM) had "placeholders". Basically, in a given area, room, or zone, mobs of one type spawn at a certain spot, and the named mobs had a small chance of spawning instead of the placeholder mob. Even in a case of multiple types of mobs having the possibility of spawning in one spot, it would go something like this:

Time for mob to spawn (depends on the "respawn" time of the zone, area, etc).
X percentage of mob A.
Y percentage of mob B.
Z percentage of mob C.

If mob B is supposed to spawn, D percentage change of NM spawning instead.

As to your theory about the moon phases or days, I say its a pretty good one, considering how tradeskills in general and also the HQ item successes are also highly tied into the day of week and phase of the moon.

If the drop theory mirrors the HQ item theory, an increased chance of spawn might occur the day BEFORE the one of the crystal the mob drops.

Very interesting subject matter.