That is a tough one to answer as it depends largely on how corrupted the hard drive is and what is used to fix the corruption. There is no common amount of time it takes.
What has happened to this internal hard drive?
In fact, a hard drive could be corrupted mechanically and logically. The mechanically corrupted hard drive is often irrecoverable, including the inner data and the physical drive. However, on the contrary, the logically corrupted hard drive does have chances to be fixed by reformatting. The inner data also could be recovered by using data recovery software before the formatting process. Read more information about logically corrupted drive data recovery: http://blog4mark.blogspot.com/2012/11/how-to-repair-corrupted-pen-drive.html