I can't see how pointing out the obvious is interesting.
although, we did neglect the part about them being once people.

but still, judging by how Grimmjaw described his path to becoming a Vasto-lord (was he one of those? or something in between gillian and vastolord?) as long and tedious, and how Brannagan recalled his eons of ruling over hell, and what's his name (#1) spoke of his lonely life at the top...
all those things seemed to take a real long time, so it's probably safe to say that the arrnacers were formed over the course of hundreds of years...

or somewhere around last June. hard to tell time in Bleach land.
maybe we'll get to see a redemption flashback of them.