I’ve seen this claim before
http://boards.straightdope.com/sdmb/showpost.php?p=5101151&postcount=33
and probably have even referred to it myself, but I don’t know whether it has ever been verified. The image of a US president hovering over a desk full of papers, fretting over tedium like this while the country is, according to him, undergoing a crisis of confidence while US territory has been seized by foreign terrorists is, well, bizarre.
The story apparently originated with James Fallows, then a speechwriter in the Carter White House: http://www.anecdotage.com/index.php?aid=13407. Every other reference to the tale would appear to go back to Fallows’ original revelation, published in The New Yorker. Remember, too, that Carter himself was an avid tennis player (maybe still is, for all I know), so getting involved in the court scheduling was perhaps a bit less bizarre than it sounds at first blush.