The light cycle. Just like us humans. When its dark for the whole day, our mood will drop and depression will rise. If the light cycle is consistent, it will maintain the mood and stress at pace despite any build up stress from the environment.
If the light is on for the whole day or during the night, the stress will build up as the crab have nowhere to hide as to them, in the nature, light is their enemy as larger crabs will hunt them for food or being "fried" by the sun. So in the day, they burrow / hide in dark areas, hole and will come out during the night.
As the light cycle keeps going on normal pace, the crabs will learn and adapt accordingly. Not to mention, they have sense of understanding and certain degree of intelligence.
One incident is the way i put their food, they know which spot i will throw and once, i saw all of them stacked on the food spot waiting

Humorous it is

Strawberry crabs is quite strong for its size, so when they adapt on something, they will keep doing it. Make sure you have your drift wood being put slightly away from the door. Soo, they have to adapt another new height and challenge.