Nintendo's official website says so.
Nintendo of America's official website now lists a Q1 2004 release date for Metal Gear Solid: The Twin Snakes. The game was previously expected to come out before the end of the year in North America.
Nintendo.com does occasionally contain errors, though we doubt it's the case here. However, PGC will be checking up on this story with Konami and Silicon Knights for confirmation and further information.
Props to Gumby at the GA Forums for spotting this one.
Update: PGC reader General Oniram pointed us to further confirmation of this report. At Konami's official Twin Snakes website, the Staff page says "Early 2004" at the bottom.