In excel dates are converted to serial number. The serial number for 9-11-01 is 37145, and the serial number for 3-11-04 is 38057. The difference between to two is 912. This means 3-11 is the 912th day after 9-11-01 (remember 2004 is a leap year). So if you do not count 9-11-2001 OR 3-11-04 then there would be 911 days between the two dates.
Everybody's been trying to get me to learn excel but I've never gotten around to it. Thanks for the info.
Do it with the times of the attacks and it is 911.72 exactly