Compassion Even for the Guilty:

Sefer Noam Elimelech asks why he pushed them off until the next morning. He answers that Moshe wanted to try to save them. He therefore told them to wait until morning, which is a time of Divine mercy – a time when Hashem's middah of chesed is revealed to the world. He knew that at this time of chesed, even guilty people receive His mercy, either because He is compassionate to all His creations at this time or in the merit of the tzadikim of the generation. He thus told them to wait until morning, when Hashem "makes known who is to Him", meaning that He has compassion on everything He created, or "the holy will be close to him", meaning that He will have mercy in the merit of the holy tzadikim and that would protect them.