If vitamin d deficient, how long does it take to get back within the normal level with just the sun and without supplements?

I'm unable to find a study that actually determined this. However, 15 minutes in the midday sun gives you enough vit D for a day. Remember that spending too much time in the sun has health risks. I think it's easier to take 1000 units of vit D3 daily and this will keep your blood level of vit D in good shape.

Not feasible to be exact. 20 minutes in sunshine without sunblock 3-4 times/week will improve levels but to reach desirable 50-70 ng/ml, it is most efficient to supplement