Reset would be purely up to the admin, hard to estimate when it may be.
Usually once havoc starts its 2-3 days. Then 1 day on paused era. Its harder to guess when havoc is going to start then when it is going to end. They will wait a few days after one world resets to put another in haovc then put that back to tick 1. Though in the end this is just personal experience from waiting and not an exact measurement. Usually you can ask an admin too and they wont mind saying the day.