No link between wake up time and income

I hadn't given this topic too much thought before, but I did find this article somewhat interesting. This study is based on a survey of individuals' wake up time and annual income. The results showed that the wake up time was no different in the highest income earners vs the lowest earners. The article goes on to say that the results of this study do not support the notion that the early bird gets the worm. I'm not so sure as other factors are not being considered in this situation.