When should I start preparing the soil for planting in the spring? Also when trying to adjust the pH of soil what is the time frame I should expect to see a change in the soil?
Late winter to early spring is a good time to start working on your soil, provided the weather is somewhat warm and the ground is workable. Here are some tips for amending soil that may help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/improving-garden-soil.htm
Note, you may not notice the pH changes right away, but certainly within a month or so with careful monitoring you should notice a change. Make sure to test both the soil and pH beforehand to help determine what changes are necessary.