⌛ How long does it take to form a habit?

The habit formation is depend on the frequency of the action, not days. You should ask ‘how many repetitions are required to make a habit automatic?’ Instead of asking ‘how many days it takes to build a habit’.

You often decide what to do next is based on what you just finished doing. Each...

1. Choose an action and an attitude that will make the highest contribution toward your goal. The actions are the daily habits that make everything else easier. The attitude is believing that it will work.
2. Give yourself instructions to follow

On average, it takes 30 to 45 minutes for your rods to be fully dark adapted to night vision. 

It also covers things such as Mesopic vision and Scotopic vision, eye health, and how to actually dark adapt. I suggest it as a good read.