Net of a large number of social and demographic factors, more intelligent children grow up to be more nocturnal as adults than less intelligent children.
Compared to their less intelligent counterparts, more intelligent individuals go do bed later on weeknights (when they have to get up at a certain time the next day) and on weekend (when they don’t), and they wake up later on weekdays (but not on weekend, for which the positive effect of childhood intelligence on adult nocturnality is not statistically significant).
For example, those with childhood IQ of less than 75 ("very dull") go to bed around 23:41 on weeknight in early adulthood, whereas those with childhood IQ of over 125 ("very bright") go to bed around 00:29.
Looking at that Sunday morning sleep-in time, I'm still trying to figure out if this article is a joke. :-)