As Blush has mentioned, a certain amount of the Honour Guards must be killed by the whole server to activate the mini-world change. The easiest way to check the status of the change is to ask any NPC Guide (every city by the ship).
Here is a transcript of their answers:
Guide: Horestis's body has been desecrated. His curse now hangs over Ankrahmun like the shadow of the vulture and his tomb is almost empty.
There are a lot of Honour Guards on the desert, the tomb is filled with Grave Robbers and Crypt Defilers.
Guide: Horestis's body has been desecrated. By now, his curse has ended though. His minions are recovering slowly.
Horestis will appear soon (in one or two days).
Guide: Horestis near Ankrahmun is slumbering in his tomb. I wouldn't disrupt his sleep if I were you - this might be better for us all. Seriously.
Horestis is in the tomb and you can attempt to break the vases.