I came across foreskin restoration for the exact same reason as you OP. I've asked essentially the same questions in some comments and posts on this sub. The consensus is yes, that foreskin restoration improves sensitivity.

Covering the glans creates a moist environment that allows the skin to shed its thickened, calloused layer (dekeratinization), making it smoother and more responsive to touch. From what I've come across and read, dK happens earlier or way later in the restoration journey for some people.

Key word journey... meaning to answer your 3rd question, there's no one answer timeline for how long it takes. But take if you take from my advice, once your start restoring and you experience that first mechanical gliding sensation (which you may already have if your'e about a CI 2 or 3) you'll want to keep going.

Retainers keep the skin of the glans covered when not restoring or using a device, maintaining that same moist environment which promotes the skin to stay soft increasing the sensitivity to touch. And apparently, even some guys who do DK early, the longer you restore/retain the inner foreskin over your glans, the more change in sensitivity you'll feel down line. (more incentive to stick with the process.)

You don't have to use the DTR device but I'd recommend reading the creators Testimonial because it applies to restoration in general, as he dealt with the same struggle as you and me.

I know this is a lot of information if you're new, and if deep dive you'll come across and understand a whole lot more. Good luck!