Any advice about my cat would be greatly appreciated?

I got a cat free to good home from a woman, he is 4 years old, when i got him she said he will be scared at first but will get better, anytime i walk past him he will slowly back away and go as far up the wall as posible in a corner he stays in the bathroom behind the sink he is that scared he stays there all day he eats and drinks fine, i leave the doors open for him to leave the bathroom when he wants to, i stoke him alot ant talk to him in a soft voice and feed him from my hands yesterday i was sitting close to him for ages feeding him treats and he finaly walked onto my lap but was digging his nails in me, today he wont even eat from my hands how long will it take for him to stop being scared? Ive had him for a week now.