That. Atlantis best launch date was February 10. Columbia crew would asphyxiate on February 15. At first glance it seems, well they have a small launch window of five days. Except that some knowledgeable engineer on a forum explained things didn't worked that way at all. A single day lost in Atlantis flight readiness didn't meant it would lift off on February 11. It rather translated into a much bigger slippage, something like two or three days lost, meaning the 5 days theorical margin was essentially non-exisiting. There were case in Shuttle history when a glitch happened only 3 seconds before liftoff pushed the flight by two months !