While the requirements for this achievement is self explanatory, it is recommended that this be obtained on a Windows 10 device if you want to finish this as quickly as possible. Because the apps were removed from the Windows 8.1/RT Store (as I had explained in the Microsoft Casual Games and Server Changes
forum), the ability to change the dates on Windows 8.1 devices to access previous challenges have been discontinued. Thus, you have no choice but to grind things out for 10 months. Fortunately, the backdating technique still works on Windows 10 and you can go back beyond two months to get this done. So I would advise that you change the time on your PC to an earlier date (disable auto update of date and time) and complete about 12-13 days of challenges for 9 previous months. They will sync when you set your PC to the correct time. After that, you can obtain the 10th medal with your PC set to the correct time which can prevent any conflicts with time stamps.