He says “okay,” but his heavy breathing continues for about ten seconds, indicating it took him about ten seconds to stop running. The accusation that he disobeyed an order to stop following Martin was invented to explain how they came in contact with each other. When you know that Zimmerman stopped running and Martin left the area, the only logical conclusion is that Martin returned.
DO I trust the media to actually sort this out? No way. Wish I had some dough to put up an animated reconstruction based solely on the 911 calls on youtube. Every now and then I lament not being rich enough. It would be $5000 well spent.