Nobody can tell you in exact terms the time needed to restore your focusing ability; it’s also very hard to estimate it, since it depends on many factors—your initial refractive state, the kind of work you are doing, your visual environment, and the kind of effort you are willing to make. Also included is time you spend using your “protective” lenses and your personal verification of results by checking your own eye chart.

I can say that the time you need to improve your sight depends on the quantity of your training and, above all else, on wearing your “preventive” glasses.

Let me explain further: if someone trains 5 minutes a day and someone else trains for 20 minutes, obviously the time they need to reach the flashes of distinct, clear vision is different. It’s useless to do the exercises and then spend all the day at a computer, wearing your minus glasses, because in such a case overaccommodative stress (proximal stress produced by the minus lens) persists. One thing is certain: the time needed to get improvements is much shorter than the time it took to worsen your sight (which induced your present dioptric prescription).

Being supervised by an optometrist or an ophthalmologist, you can start to do cyclorotation: slow and concentrated on the present maximum range of your eyes, and symmetric. Later on, you can start doing the exercises on retinal defocus so as to bring about a better refractive state. As for this, you should take advice from your physician.