How to create Timer animations?

I am assuming that when you write about Timer you talk about a visual element in your GUI that looks like a physical timer/chronograph/stopwatch type of thing, i.e. http://openclipart.org/detail/125725/time--temps-by-lmproulx, and that for animation you generically mean the way it changes over time (as opposed to a more specifically defined Unity Animation object).

The timer accuracy is dependent on the method you use to switch from one frame to the next rather than the method you use to create your asset. I.e. 2Dtoolkit seems to have its own way to set the frame per seconds of a sprite-based animation.

Personally, unless I needed some really fancy graphics that requires individually painted sprites, I'd do it with a 3D asset consisting of a circular frame and a number of wedge-shaped internal slices. I'd then use a simple script to hide each wedge, in order, as the time ticks.