WASHINGTON (Reuters) – President Barack Obama said Saturday more time was needed for his $787 billion stimulus package to work, predicting the spending would have a bigger impact on the economy later this year. In an advanced text of his weekly radio speech, Obama said the stimulus plan approved by Congress and signed into law in mid-February "was not designed to work in four months -- it was designed to work over two years." U.S. Treasury Secretary Timothy Geithner said it was too soon to decide whether the U.S. economy needed the help of a second-round of government stimulus to...