Timed Wither Storm
This datapack completely changes the standard Wither Storm spawning mechanism. Instead of appearing at a fixed time of day, it will begin forming after a certain interval of in-game time, and its appearance will occur at a significant distance from coordinates 0,0.
You can flexibly configure the timer behavior using the '/trigger WitherStormControls' command in creative mode with operator privileges. Available functions include changing the countdown duration, pausing, or completely resetting the timer.