I saw him practice up close in Miami. He took up the whole hour. But I don't think he ever broke a sweat, seemed to be enjoying himself and fully relaxed (until he broke his racquet on court
). This is in contrast to Rafa, whom I also watched up close - he was training with Del Potro - they were working very hard, with uncle Tony watching every shot... a lot of the players I watched train up-close (murray, roddick, blake, safin, youzhny, & few more) seemed to take their practice a bit more seriously than him... but that could have just been my perception of his training, as he does tend to make tennis look very easy.