It is correct but "earlier" is better unless you are making a comparison: "Before noon I received this letter". "Earlier" works well as a synonym for "some time ago". "Before" does not work quite as well that way. Conversely, "earlier" does not work quite as well for comparisons. You can say "earlier than noon I received this letter" but "before noon" sounds a little bit better.

できますが、「Earlier」のほうがもっと自然です。