Turn of Time is first and foremost an abstract game so the theme is rather weak. Nevertheless, the concepts of seasons and time are useful for learning and understanding the game mechanisms.
The circular relations between the players is the key mechanism of Turn of Time. In a game like Iconoclasm, where the players play the four elements, this relation is not obvious (why does fire support earth and not, say, air?). However, everybody knows that Spring eventually will beat Winter so here the circular relations make more sense. As a matter of fact, this is even better than a completely abstract relation between the colors green, yellow, red and blue. Moreover, the theme of changing seasons fit very well with the theme of time.
Time is a theme of the game and what is a good symbol of time if not a clock? In the game, a turn of a time is symbolized by the clockwise turn of a game mat, bringing the next season in order one step forward (or backward). It's a simple yet powerful implementation of time in a game.