http://www.onlineconversion.com/julian_date.htm

This tool convers to Julian time which is used by Google in its DATERANGE function

for TODAYS date June 25 2006
   just add
Daterange:24539116187

Fagan finder has a online converter – but it ends in 2004
   but may still be helpful for proper formating of operators

http://www.faganfinder.com/engines/google.shtml