If they are next to each other in the queue, then you choose the order, but not if there is an enemy or friendly NPC in between (anything controlled by AI). If you select the last controllable character that is available to you, be sure to not end that character's turn, though, as that will end the turn for all characters that "go together".
From your topic I'm not sure if you want to be able to "delay" it in the sense mentionen above or if you want it to be placed last in the queue.
