Killed Antlion on day 2 of summer , day 4 entered caves to farm nightmare fuel and at around 5-6 days in the caves I got a cave in. 2nd to last day of summer I got the surface craters. I went to check Antlion and sure enough she was there.
Edit: it was raining when I entered the caves thus stopping the sandstorm, don't know if that may be a factor
Kill Antlion and spelunk