Is it possible that people who lack self-control also have a poor sleep schedule? I know that I personally can be rather poor at telling myself to go to bed…
I think the point the article is making is that if you want to reduce your procrastination, you should first try to regulate your sleep. Procrastinators who get a good night's sleep, will have a better chance of not procrastinating.
From a shallow skim, it looks like this study compared the same people across multiple days.
That's also why I end up here half the time.. back to work.