There's an evolutionary reason why some people are early risers and others like to stay up late.
The families that survived in the Palaeolithic were the ones that had someone always awake to watch out for leopards and other predators that found these funny, furry, slow and defenceless apes remarkably tasty. The families that all went to sleep at the same time got eaten, and so didn't pass on the genes that regulate for different sleep patterns.