How long until my cat grows back his fur?

My cat had a skin condition which made lots of his fur fall out, the vet gave him injections before and after Christmas and his fur seems to be growing back, but he is still bare at the back of his hind legs. Does anyone know how long it normally takes for a cat's fur to grow back ? He's a black domestic shorthair and is 8 years old and neutered.
We had his blood tested for anything more serious but the test was negative.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).