How long after a vitrectomy does it take for the silicone oil bubble to be surgically removed and vision to return?

This depends: This depends on the stability of your retinal problem and the practice of the doctor. For certain problems, like retinal detachment from proliferative vitreoretinopathy silicone oil is left in 6-12 weeks. This is a minimum. Patients with "severe" problems can have silicone kept in for much longer. Discuss this with your surgeon.