How badly the nerve is injured will affect how fast it can recover. If a nerve is cut in half and sewn together, it can grow at the rate of an inch a month or a millimeter a day. If the nerve is mildly pinched but still functional, then it can recover function in a few hours or a few days.
As the nerve compression gets more severe or if it has been compressed a long time, it can take months for nerves to improve. The nerve will regenerate better in younger patients than in older patients. However, we do see nerve regeneration and functional improvement even in the elderly.