Oda has introduced the concept of the Sun God, and likened his design to Luffy back on Skypiea.
Dawn is fast approaching over this raid battle, which is the perfect time to coincide with Kaido's defeat. The sun rising/Bringing the Dawn/Defeating Kaido.
Luffy has already done something similar to this on Skypiea when Enel darkened the sky with Riago, and Luffy destroyed it, exposing the sun.
He also did something similar on Thriller Bark by defeating Moriah just before the sun rose, killing everyone.
Zorofans: "Symbolism, and foreshadowing be damned, Zoro is going to be the one to finish Kaido off."