For a reference point, we did a Full Format of a brand new WD Green 1.5 TB drive recently and it took about 3½ hours. Some might be a bit longer or shorter. On an older drive the times will be longer, perhaps, than this. But your situation certainly sounded like a bad drive with loads of errors, and that is what your buddy diagnosed.
A Quick Format DOES do all of the essential format job for you in less than 15 minutes. However, a Full Format does that part and THEN does exhaustive read / writes tests on EVERY sector of the disk, which is what takes all the extra time.