...If I remember correctly, there are many monsters in the desert that are active at night.
Moving around in the darkness, I'm sure getting surprise attacked by monsters would be dangerous.
"Elinalise-san, what should we do?"
"Even if we started walking now, we wouldn't cover very much distance. It's a bit early, but let's sleep in a place with a roof."
It became that we would be staying over night in these ruins for today.