I was playing on normal, and I found that I had time to maybe cultivate and make one pill each time at most and it wasn't enough.
It's possible that I could have done a bit more if I had let the monsters beat on my base. But that doesn't feel intuitive. Especially since the tutorial is pretty insistent on responding quickly.
Monks were also completely useless. They got deleted by enemies instantly. I stopped rehiring them after wave 4 because it felt like a waste of spirit stones.