“Is it important to introduce and explain your philosophy early in your autobiography?”
I believe this depends on your writing style. If you can incorporate your philosophy with coherency and logic throughout your book, then it is not important or necessary to introduce your philosophy early in the book.
If you introduce your philosophy early the reader can decide if they actually want to read the autobiography. When I read the autobiography of Henry David Thoreau, Walden, I found that his philosophy was scattered chaotically throughout his book, therefore making it hard to make ‘head-or-tail’ out of it.
Whether or not you explain your philosophy early in the autobiography really depends on your writing style.