Personally, the period of time is different for different people. I always adjust the darkness after several minutes. But i saw it online that it takes approximately 20-30 minutes to fully adapt from bright sunlight to complete darkness. Maybe your can try yourself to see how much time you need to adjust the change of environment.
It is said that the adjusting time from bright place to the darkness is different for different people. Usually people will need two or three seconds to adjust to the new dark environment. But it is not exact for everyone. Even the time is a little longer. That is OK. This is decided by our physique.
It takes about three seconds for our eyes to adjust to darkness when walking outside into the dark. There are cone cells and rods in retina. Cone cells can feel the strong lights from outside compared with rods that are sensitive of weak light. When we are in dark, we see things depending on the rods and cone cells will out of action. Rods contain rhodospsin. Rhodospsin will resolved in bright light. So when people get into the dark, cone rods are out of work and rods are needed to novo synthesis rhodospin. This process needs time. It usually take about three seconds. That is why people must spend about three minutes adjusting to darkness.
It takes about 5 to 10 minutes to fully adapt from bright lights inside to complete darkness outside. Human vision has the incredible range of light, thus we can see in very birght sunlight, and we can also see in nearly total darness. The reason why we can see from bright lights to dark lights totally depend on two cells of eyes. The first one is called rod cells that is located in the retina, which can preceive black and white images and work best in low light. The other one is rhodopsin that is a chemical found in the rods and is the key to night vision. Due to it can absorb photons and preceive light.