$InstallationDate
$InstallationDate gives the date and time at which the copy of the Mathematica kernel you are running was installed.
$InstallationDate is in the form year, month, day, hour, minute, second returned by Date. See The Mathematica Book: Section 2.13.5. See also: $CreationDate.
$InstallationDate gives the date and time at which the copy of the Mathematica kernel you are running was installed. 
year, month, day, hour, minute, second
returned by Date. 
