// 7:32:56 pm on May 10, 1965
$epoch_1 = mktime(19,32,56,5,10,1965);
// 4:29:11 am on November 20, 1962
$epoch_2 = mktime(4,29,11,11,20,1962);
$diff_seconds = $epoch_1 - $epoch_2;
$diff_weeks = floor($diff_seconds/604800);
$diff_seconds -= $diff_weeks * 604800;
$diff_days = floor($diff_seconds/86400);
$diff_seconds -= $diff_days * 86400;
$diff_hours = floor($diff_seconds/3600);
$diff_seconds -= $diff_hours * 3600;
$diff_minutes = floor($diff_seconds/60);
$diff_seconds -= $diff_minutes * 60;
print "The two dates have $diff_weeks weeks, $diff_days days, ";
print "$diff_hours hours, $diff_minutes minutes, and $diff_seconds ";
print "seconds elapsed between them.";
**The two dates have 128 weeks, 6 days, 14 hours, 3 minutes,**
**and 45 seconds elapsed between them.**

Note that the difference isn't divided into larger
chunks than weeks (i.e., months or years) because those chunks have
variable length and wouldn't give an accurate count
of the time difference calculated.