There is never a good time for management to sell stock. When management sold in the 60's, there was a hue and cry from some shareholders. If they had sold in the 30s, the ensuing panic would have caused the stock to go all the way down to the 20s.
Of course, people prefer that management never sell stock, and to just be content with their half-a-million salary even though their options are worth tens or even hundreds of millions of dollars.
Sergey Brin sold lots of stock just last week, when Google's share price is at its one year low. Even he must know that Google is actually undervalued at the prices that he sold at. But then again, when is it ever a good time?