I know trying to work out exact dates for comics continuity is pointless, but it’s fun.
So, assuming Kate Kane is currently 29 in the DCU and her birthday is March 21st, and with a bit of other research, I figured out some exact dates for certain events in her life, given what we currently know (as best as I can tell, anyway).
Monday, March 21, 1988 - Kate and Beth Kane are born.
Tuesday, March 21, 2000 - Kate, Beth, and Gabi Kane are kidnapped. At approximately 8:35 PM local time, Gabi is killed in a rescue attempt.
Thursday, September 11, 2008 - Kate has a private sparring match with Sophie Moore (this one is iffier, admittedly).
Friday, September 12, 2008 - Kate receives her class ring.
Saturday, September 13, 2008 - Kate leaves West Point.
Monday, September 15, 2008 - Kate comes out to Jacob.
Saturday, May 23, 2009 - West Point Class of 2009 graduation.