Condensed from Ein Ayah, Shabbat 9:16 Unadulterated Heavenly Inspiration
Moshe went up [to Sinai to receive the Torah] in the beginning of the morning, and he came down from the mountain [with the Torah] early in the morning. The fact that he went up early is learned from that which it says: “Moshe woke up early in the morning and he ascended to Mt. Sinai” (Shemot 34:4). The fact that he came down early is learned from the pasuk, “Go, come down, and you shall go up, you and Aharon with you” (ibid. 19:24). The descent is connected to the ascent – just as the ascent was early in the morning, so too the descent was early in the morning.