Why did Long Silver put off the mutiny for so long?

Frankly, Silver doesn't know the exact location..... and he needs all the men to find it and get it on board.

"When! By the powers!" cried Silver. "Well now, if you want to know, I'll tell you when. The last moment I can manage, and that's when. Here's a first-rate seaman, Cap'n Smollett, sails the blessed ship for us. Here's this squire and doctor with a map and such—I don't know where it is, do I? No more do you, says you. Well then, I mean this squire and doctor shall find the stuff, and help us to get it aboard, by the powers.