How fast will a solar cover heat an above ground pool?

Technically it won't heat the pool (and in some cases slows the heating process), but it helps to prevent it from cooling as quickly. Below is the best link that I was able to find that explains all aspects of allowing your pool to heat naturally and "trapping" the heat in. There are way too many variables to answer the question with an actual number, but you should be able to get a pretty good idea here.