I'm rather surprised to see this statement: "...our planet has operated on a 24-hour clock for the entire span of evolutionary time". My understanding is that

I'm rather surprised to see this statement: "...our planet has operated on a 24-hour clock for the entire span of evolutionary time". My understanding is that during the Cambrian, the day was less than 23 hours long. At the emergence of the first eukaryotes it was 21 hours. Much shorter still when life first appeared. That makes the uniformity of this protein across the major branches of life quite fascinating.