How long does it take to fully heal a retinal detachment?

Depends. It depends on the technique used to treat it, for example it takes at least 2 weeks for laser treatment to reach maximum strength in adhering the retina, so if an in office procedure was done, this would be the minimum time to heal. More invasive surgeries require longer healing times.
Several weeks. It can take 2-6 weeks to completely heal. During part of this time it may be critical to maintain a certain head position, depending on the type of repair you have.
Depends on repair. Some retinal detachment repairs involving a gas bubble can take up to eight weeks to heal. Others can be fairly well-healed within a couple of weeks. For someone who is young like you the possibility of further problems exist later so follow up with your ophthalmologist over time is critical.