The three factors that most greatly contribute to length of a Zimby Mojo game are:
1) how well the players cooperate to kill the King quickly,
2) how similarly skilled the players are,
3) how strategically the players approach the end game.
The first factor affects the length of Part I of the game (the deliberate, cooperative part); the second and third factors affect the length of Part II of the game (the free-for-all, chaotic part). This variant -- Be a Zimby! -- is designed to reduce the length of Part II.
Be a Zimby!
Zimbies are frenetic, vicious, compulsive, and somewhat inept little creatures. They don't put a lot of thought into their actions and thrive on chaos and combat. This is why shamans must expend mojo to control them and force them to follow directions. That said, a shaman is still a zimby, so...
... why not encourage player's to act like one?
In this variant, the players use a 1-minute timer* (a sand timer, phone timer, egg timer, etc.) to limit their turn length once the King dies. After the King dies, each player has just 1 minute* to complete their individual turn. This limits players' time to think about their resources, strategy, etc. and forces them to act swiftly -- and potentially ineptly -- in the wanton chaos that reigns upon the King's death. Basically, everyone acts more like a zimby!
Not only does this variant increase the fun and frenzy of Part II, but it can also significantly reduce its length. I hope that you find this variant useful and look forward to reading your session reports!
* NOTE: You may want to start with a 2 minute time limit to ease into this variant!