A new study had people try to get into the habit of doing a simple, 15-second stretch every day. Half of them did it in the morning, right after they woke up. The other half had to do it at night, before they went to bed.
And the ones who stretched in the morning started doing it out of habit a lot sooner than the ones who stretched at night.
The morning group started doing it without even thinking after 105 days. For the people who did it at night, it took 154 days before it became a habit. So that's almost 50% longer.
The authors of the study think it has to do with the stress hormone cortisol.
Other studies have shown a link between cortisol levels and forming habits. And there's much more cortisol in your body in the morning than there is at night.
(Time)