Rule 721.2b

Each other player, in turn order starting after the player who suggested the shortcut, may either accept the proposed sequence, or shorten it by naming a place where they will make a game choice that’s different than what’s been proposed. (The player doesn’t need to specify at this time what the new choice will be.) This place becomes the new ending point of the proposed sequence. Example: The active player draws a card during her draw step, then says, “Go.” The nonactive player is holding Into the Fray (an instant that says “Target creature attacks this turn if able”) and says, “I’d like to cast a spell during your beginning of combat step.” The current proposed shortcut is that all players pass priority at all opportunities during the turn until the nonactive player has priority during the beginning of combat step.

Find this number in the current Rules