What condition does steelkilt place on the obedience of the crewmen who have joined him?

Steelkilt's condition was that he be the first to burst upon the deck.

"And what was more, they each insisted upon being the first man on deck, when the time to make the rush should come. But to this their leader as fiercely objected, reserving that priority for himself; particularly as his two comrades would not yield, the one to the other, in the matter; and both of them could not be first, for the ladder would but admit one man at a time. And here, gentlemen, the foul play of these miscreants must come out."