If you right click the file you've donwloaded to extract it, you'll see there's a file calles 'As_it_reaches_zetta.ttf' That's the timer font file. If you're using windows Vista or 7 you just need to double click it and at the top left corner of the font preview window that will show up, click the Install button.

If you're using another Windows OS, go to control panel open the Fonts folder and just grab and drop the ttf file inside the Fonts folder. (Note that this will work in Vista/7 too but it's easier the other way, isn't it?).

Now just open the software in which you want to use the timer font, just select it from the dropdown menu of available fonts you have. Not that it's named 'As It Reaches Zetta' so it should be pretty up in your font list.

Hope you find this helpful.