how long to get used to single vision eyeglasses?

Because you were used to vision with contacts and suddenly switched to pretty strong glasses, you are really going to notice a difference. The glasses are probably OK; when you wear fairly strong glasses, there is going to be some distortion at the edges of your visual field. This is because when you are not looking straight ahead, you are not looking through the exact center of your lenses. This effect is much less with contacts because the lens sits right on your eye and moves with it. For strong negative prescriptions, things tend to distort in a "convex" manner (i.e. when you approach a doorway it will go barrel-shaped). Things like telephone poles go banana-shaped unless you look straight at them. Flat hoizontal surfaces will appear to bow upwards in the center if they are in your field of view above the center of your lenses, if they are below the center, they will bow downwards in the middle. You will probably notice, at night, if you look at a street light out of the corner of your eye, that the light is partly broken up into its spectrum, this is because the lens also acts like a prizm when you are looking through it off-center. My glasses do the same thing. Most of the time this is not a big deal as people usually turn their head rather than look out of the corner of their eyes. After you wear you glasses for a while, your brain will get somewhat used to the distortions, but it will never be as distortion-free as with contacts.

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Should not take more than a week or 2 to get used to it.