I managed to produce what I am looking for. Here is the code for it, if someone needs it:
static String fn_Z_getTimeDifference(Long startTime, Long endTime)
{
long processTime = endTime - startTime;
long days = processTime / 86400000L;
processTime -= days * 86400000L;
long hours = processTime / 3600000L;
processTime -= hours * 3600000L;
long mins = processTime / 60000L;
processTime -= mins * 60000L;
long seconds = processTime / 1000L;
processTime -= seconds * 1000L;
long milliSeconds = processTime ;
return (Long.toString(hours)+ ":" + Long.toString(mins) + ":" + Long.toString(seconds) + ":" + Long.toString(milliSeconds)).toString();
}