Something like this:
#include <date.au3>
Global $sTime1 = "13:43:24", $sTime2 = "13:44:35"
Global $iTime1, $iTime2
Global $aTemp, $sHour, $sMinute, $sSecond
$aTemp = StringSplit($sTime1, ":")
$iTime1 = _TimeToTicks($aTemp[1], $aTemp[2], $aTemp[3])
$aTemp = StringSplit($sTime2, ":")
$iTime2 = _TimeToTicks($aTemp[1], $aTemp[2], $aTemp[3])
_TicksToTime($iTime2-$iTime1, $sHour, $sMinute, $sSecond)
ConsoleWrite($sHour & ":" & $sMinute & ":" & $sSecond & @LF)