Well no kidding ultimately he will be judged on his entire time in office but the nature of the beast is people want immediate results (not saying that's fair of course because it isn't). Obama also made comments to the effect of the stimulus is going to show immediate effects and therefore reasonable people can make judgements on its immediate results that Obama referenced.
And immideatly the rate of unemployment losses decreaased. Also immideatly the stock market began to make some modist increases.