Still not catching the start/stop time. Something is left out after the file code (v=nRz9aQNmaS0).
Work some moar.
https://www.youtube.com/embed/nRz9aQNmaS0?start=53&end=59
https://www.youtube.com/embed/nRz9aQNmaS0?start=53&end=59
Sum documentation for you:
https://developers.google.com/youtube/player_parameters?csw=1