At first I didn't know that I could shoot ice pucks to refill holes, so I went around rescuing people in the holes. By the time I saved everyone, there was still 40 seconds with nothing left to do.
On my second attempt, I tried fixing the ice like I was supposed to, but eventually, I couldn't keep up, and people fell into holes anyway. It seems like the most effective strategy for saving as many people as possible is to just not bother with fixing the holes and to just rescue people when they get stuck. Perhaps a scoring system that rewards fixing holes could balance this?
Also, that game over screen is too relatable...