If you read the comments in Allah it might help. ***Khati Sha is spawned by completing the script with the arcanist's in the jail area ***Khati sha is only killable ONCE A WEEK ***So you can attempt the script every 12 hours but you will not get past the last seal to khati sha unless that 7 day timer is met.
It might help, but in this case it doesn't. It's much less than a 7 day timer. Somewhere around 60-72 hours or so. Also this doesn't address the question the OP is asking, which is whether or not there is a way to tell if Khati is available before doing the first part of the event. There is not that I know of.
It would be nice if they tossed in an NPC similar to Thylex for these types of spawns. MAoE has the same "issue" once PoP rolls around.