How to calculate the difference between two date parameters in minutes ?

In order to accomplish the above you need to write the following code:-

DECLARE FUNCTION DateDiff( $D1 PRIMITIVE, $D2 PRIMITIVE) PRIMITIVE
{
 DECLARE VARIABLE $N1 INTEGER;
 DECLARE VARIABLE $N2 INTEGER;
 DECLARE VARIABLE $REZ INTEGER;
 $N1 = $D1;
 $N2 = $D2;
 IF $N1 > $N2 {
   $REZ = ($N1 - $N2 ) / 60;
 }
 ELSE {
   $REZ = ($N2 - $N1 ) / 60;
 }
  RETURN $REZ;
}

Example:-
Test Code
DECLARE VARIABLE $x1 DATE;
DECLARE VARIABLE $x2 DATE;

$DateFormat="%Y-%m-%d %H:%M";
$x1 = "2007-09-14 08:16:00";
$x2 = "2007-09-15 23:59:00";

PRINT $x1 & " - " & $x2 & " = " & DateDiff($x2, $x1)& "\r\n";

The result will be:

2007-09-14 08:16 - 2007-09-15 23:59 = 2383