I got very good luck in this run, but I also did a few improvements to the strategy over the previous record:

I chose Shiva as my personal diety for the -10% Core Creation cost, which also reduces coring time; I took measures to reduce my war exhaustion as much as possible before coring, also to reduce coring time; I also declared war on Kathmandu before Limbuwan, since that way I could reach the forts I had to besiege as quickly as possible without wasting more time than necessary; And finally I built spy networks in both Kathmandu and Limbuwan, which should've sped up the sieges slightly.

But I also got incredibly lucky in that Kathmandu didn't get any allies, and I had pretty good luck on the forts as well, so that definitely contributed. My biggest mistake was that I underestimated my need for admin power, which could easily have been avoided and would've saved another month. Oh well.