A new study showed that the best time of day for creativity is different following the type of a person.
Wieth and Zacks(2012) had participants take two different types of creativity test. One measured their insight ability and the other measured their ability to solve analytic problems. As a result, it was found that morning-types were better at solving insight problems in the evening and evening types were better in the morning.
It is probably because being a bit sleepy and vague boadens the mind's focus.