I could be wrong (I'm certainly no investor), but rather than trying to time a large sell at the peak, I think a smart investor would accpet that prediciting stock movement that accurately is hard and actually just sell slowly over time at a fixed rate to dollar cost average their exit.
That would also have the advantage of not drastically affecting stock prices through the act of selling, since if investors know the Gates Foundation sells n shares a month come what may those sales can effectively be ignored.
