The freezer doesn't magically make food fresher. It only slows the enzyme action. If you freeze your turkey soon after cooking, you should have a solid 2-3 days to use it after thawing. However, if you freeze your turkey near the end of the 4-day window, you'll need to make sure you use it immediately when you do pull it from the freezer. Check out this great guide about Food Safety Basics from the USDA.