So chapter 4 on the highest difficulty is essentially impossible. The queen just dies before you can get there. I think it might be theoretically possible with save spamming and manipulating the rng to try to get misses from the warlocks, but that's a bit beyond the scope of what should be required.
It probably makes the most sense to fiddle around with the green units scaling with difficulty to get enough of a delay that it isn't just an rng grind. It's important to note that the difficulty scaling hurts you twice on this level: tankier enemies make it harder to rush, and more enemy dps shortens the timer.