"...more commonly spelled "Cronus" or "Kronos", was the leader and the youngest of the first generation of Titans in Greek mythology. His symbol was that of a sickle. Cronus is often confused with Chronos, the personification of time..." -wikipedia
When we started concepting for Wrath of the Titans I thought of Kronos as a much more abstract creature than it happens to appear in the movie now. Later, when the script started evolving there was a need for a little more interaction between the titans and I guess that was the time when he got a proper set of hands and eyes. Here are some early sketches from summer 2010.
MPC spared no effort to bring the character to life. One of the texture artists even covered himself with mud, while the others blasted him with hair dryers to study the moving surface of volcano skin. CGSociety published an article about the making of Kronos with images throughout the different stages of the process.