Some people go by the rule of waiting one month for every year of marriage. Although I am not sure when the one month starts: date of separation or date of divorce or other?
Honestly though, it really depends on the person. Some are ready right away. Others may never be ready. You could always just go out and test the waters. Some fun dates are okay just to take your mind of things... and yah just never know...
I would think that if you wait too long you might get harder to get back in the game.
I would always caution that if you begin dating before everything, and I mean EVERYTHING is finalized, signed and ordered, you could be opening yourself up to extensive litigation.