When you first introduce an anenome into your tank, it usually move to a shady spot , under rock, cave or area with no light because it reacting to the change (lighting, water flow, tank condition (mature tank is a must)). Anenome can't really adjust to the enviroment like some fish do that is why lighting and water condition need to be excellent. It needs to have that..can't adjust to the low lighting or just ok water condition. It mights look fine for the first few months but it will slowly wasting away
Remember, anenome is an animal so just like adding new fish, when you put a new fish in the tank...it doesn't swim around right away..it usually hide in a shady place somewhere. Everyone places their anenome right under the light in the center spot of the tank when first introduce to the tank but if your lighting is diff from the shop where you buy it from or water flow are different
..it will move around or hide and later on it will find a spot on its own to settle and stay there for a while. As how long it will be in the shadow? it is all depends on each anenome responses
to your tank condition.