Custom Clock Tile is a free app that helps you in this regard
There are many ways to customize the Windows 8 Start Screen, but in case you’re looking for a quick way to bring the time on a live tile, this app is the right choice for you.Called Custom Clock Tile, the application features colorful backgrounds and several fonts, so you can easily configure the tile’s design with just a few clicks or taps.
One of the best things about it is that it’s extremely easy to use, so you shouldn’t spend too much time figuring out which feature is which.
It provides support for all Windows 8 versions, so it can be used on desktop computers running the x86 or the x64 build of the new software, or straight on a Windows RT tablet with touch support.
Click here to view the Custom Clock Tile product page in your browser.