Converts system time difference between TimeCycle's start and end time to
hh:mm:ss format.
     
    getTimeSpan(start, end)
    Arguments
    
    
    
      | start | a numericdefining the algorithm start time. | 
    
      | end | a numericdefining the algorithm end time. | 
    
    Value
    a numeric defining the algorithm run time.
    Examples
    #> [1] "00:10:00"