Been spending more time in SRO and was able to confirm that the AC indeed will only spawn at 9PM, and the spawn rate is about 5%.
A big change from 2001, when people were reporting it being a triggered spawn with some reports of back to back sightings.
http://web.archive.org/web/200106192....shtml?id=3452
So, apparently it's not just a matter of bad luck or not getting it on the first few tries... It really is messed up.
If you don't believe me, go see for yourself...