code:

---

;FUNCTION      DateTimeDiff
;
;ACTION        Calculates the time difference between two date-times-groups
;
;AUTHOR        Jens Meyer (sealeopard@usa.net)
;
;VERSION       1.1
;
;KIXTART       4.20
;
;SYNTAX        DATETIMEDIFF(DTG1 [,DTG2])
;
;PARAMETYERS   DTG1
;              Required string as a date-time-group (DTG) in one of the following formats:
;              "YYYY/MM/DD HH:MM[:SS.MSECS]"
;              "YYYY/MM/DD" which assumes that HH:MM[:SS.MSECS] = 00:00:00.000
;              "HH:MM[:SS.MSECS]" which assumes that "YYY/MM/DD" = @DATE
;
;              DTG2
;              Optional string as date-time-group (DTG) in one of the following formats:
;              "YYYY/MM/DD HH:MM[:SS.MSECS]"
;              "YYYY/MM/DD" which assumes that HH:MM[:SS.MSECS] = @TIME
;              "HH:MM[:SS.MSECS]" which assumes that "YYY/MM/DD" = @DATE
;              DTG2 will default to the current date and time if not provided in the form of
;              @DATE+' ' +@TIME+'.'+@MSECS
;
;
;
;RETURNS       Returns difference DTG2-DTG1 as "YYYY/MM/DD HH:MM[:SS.MSECS]"
;
;REMARKS       none
;
;DEPENDENCIES  SERIALTIME() @ http://www.kixtart.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=12&t=000039
;              SERIALDATE() @ http://www.kixtart.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=12&t=000089
;
;EXAMPLE       $rc=DATETIMEDIFF('23:20:33','01:01:01.245')
;
;KIXTART BBS   http://www.kixtart.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=12&t=000374
;
function datetimediff($time1,$time2)
  Dim $date1, $date2, $datediff, $timediff

  $datetimediff=''

  if not instr($time1,' ')
    select
    case instr($time1,'/')
      $time1=$time1+' 00:00:00.000'
    case instr($time1,':')
      $time1=@DATE+' '+$time1
    case 1
      exit 87
    endselect
  endif

  if not instr($time2,' ')
    select
    case instr($time2,'/')
      $time2=$time2+' '+@TIME+'.'+right('000'+@MSECS,3)
    case instr($time2,':')
      $time2=@DATE+' '+$time2
    case 1
      $time2=@DATE+' '+@TIME+'.'+right('000'+@MSECS,3)
    endselect
  endif

  $time1=split($time1,' ')
  $date1=$time1[0]
  $time1=$time1[1]
  $time2=split($time2,' ')
  $date2=$time2[0]
  $time2=$time2[1]

  $datediff=serialdate($date2)-serialdate($date1)
  $timediff=serialtime($time2)-serialtime($time1)
  if $timediff=>86400
    $timediff=$timediff-86400
    $datediff=$datediff+1
  endif
  $datediff=serialdate(serialdate('0000/00/00')+$datediff-1)
  $timediff=serialtime($timediff)

  $datetimediff=$datediff+' '+$timediff
  exit 0
endfunction

---

 datetimediff("2005/03/04 15:00:16","2005/03/07 14:20:12") 

function datetimediff($time1,$time2)
  Dim $date1, $date2, $datediff, $timediff

  $datetimediff=''

  if not instr($time1,' ')
    select
    case instr($time1,'/')
      $time1=$time1+' 00:00:00.000'
    case instr($time1,':')
      $time1=@DATE+' '+$time1
    case 1
      exit 87
    endselect
  endif

  if not instr($time2,' ')
    select
    case instr($time2,'/')
      $time2=$time2+' '+@TIME+'.'+right('000'+@MSECS,3)
    case instr($time2,':')
      $time2=@DATE+' '+$time2
    case 1
      $time2=@DATE+' '+@TIME+'.'+right('000'+@MSECS,3)
    endselect
  endif

  $time1=split($time1,' ')
  $date1=$time1[0]
  $time1=$time1[1]
  $time2=split($time2,' ')
  $date2=$time2[0]
  $time2=$time2[1]

  $datediff=serialdate($date2)-serialdate($date1)
  $timediff=serialtime($time2)-serialtime($time1)
  
  ; added to handle negative values from $timediff
  if $timediff<0
  	$datediff=$datediff-1
  	$timediff=$timediff+86400 ;adding the negative and a positive give the proper diff 
  endif
  ; end addition
  
  if $timediff=>86400
    $timediff=$timediff-86400
    $datediff=$datediff+1
  endif
  $datediff=serialdate(serialdate('0000/00/00')+$datediff-1)
  $timediff=serialtime($timediff)
  $datetimediff=$datediff+' '+$timediff
  exit 0
endfunction