Things You Never Noticed VII: Wait, This Isnt the MitD Thread?

[understatement]

Not really, Xykon moved into the dungeon pretty much immediately after killing Dorukan per Start of Darkness. Maybe it took a while before Celia noticed him and his minions.
Keep in mind that Celia's first appearance predates the Snarl plot, so any inconsistencies with later stories do not necessarily have a deeper meaning.

EDIT: Whoops, I think I thought it out wrong. Assuming he doesn't renew the spell during his reign in the Dungeon, Xykon would be a minimum(?) of 26-27.

At the same time, I can't find a reason why Xykon would wait, say, any interval of time after mastering an epic spell. Does the SRD mention a minimum amount of time a sorcerer can learn an epic spell?