How long is it supposed to it take for severe damage to be done with macular degeneration?

Varies: Macular degeneration is variable from case to case. Prediction of the course of the damage is not easily done and is likely to be wrong. Just make sure you are seeing a retinal specialist in ophthalmology who can monitor this and give you treatment when needed.

Usually years: Depends if it is the dry type or wet type - wet type is more aggressive and patients can have submacular hemorrhage with sudden loss of vision; but usually amd takes many years to affect the vision; also depends on if the retinal atrophy is outside of the fovea (center of macula), so vision can be quite good for long time.