Collagen can begin forming around silicone, which has been implanted or injected into the lips, within weeks. However, I would strongly reccomend against having liquid silicone injected into the lips. If an infection were to occur, it would be very difficut to remove the silicone and could result in a significant deformity. A better and safer option would be a hyaluronic acid filler, Restylane, or free fat injections. Solid lip implants are available, but may also need to be removed should an infection occur.