If you suddenly give a large cat that you've had for a long time a new owner, it will definitely be difficult for the cat to accept it quickly. The cat is already familiar with its previous living environment and may even have recognized its owner. If it is suddenly given to someone else, it may feel abandoned by its owner and will not only be very frightened in the new environment, but also very sad. 
It generally takes about a month for an adult cat to get used to a new environment and owner. Moreover, each cat has a different personality, some are faster and some are slower. You must be patient and use the right guidance methods to prevent the cat from refusing to eat.
Every cat is different, especially adult cats, which tend to adapt less quickly than kittens. Some cats adapt to a new environment and owner in 3-5 days, while others may take longer. As long as the owner spends time playing with the cat and provides treats or snacks, it will adapt relatively quickly.
