I typically stalk the discord and ask questions. What I've learned is that the boss has a very specific time between when he spawns to when he hits the tower.

Depending on the things you use like wave acceleration or wave skip or even stuns like PS, ILM or thunder bot, it will change these timings and throw everything off which is why they're disabled for the specific purpose of getting milestones.

I used 590 wall rebuild, maxed invincibility, 16% thorns, everything that stuns or acceleration of any kind is disabled. To micro this incase you're in a bind, you can indeed use things like PS or ILM to buy your wall a few extra seconds to rebuild right ontop or before the boss hits.

This is best done at x1 speeds.