How long does it takes for a fish to adapt to its new home?

I bought a giant danio (to accompany my other 2 giant danios), 3 steel-blue lyretail 3 days ago. Along with these 4 fish, the shop owner gave me 1 fish for free. It's around 6-7 cm (including the tail) and has lime green tail and fins and the half of its body is also lime green, the rest of the body is grey. Has greenish eyes. For 3 days, this fish had been sulking in the dark side of the tank. In the shop this fish is also the only one of the species. But in my tank. It's just sulking and doing nothing. How long will the sulking last? How long will it take to adapt to its new place? and if you know what kind of fish is that, please tell me because when the shopkeeper told me the name of the fish I can't hear him clearly. and also, there's no signs of diseases