Difference between two timestamps in SQL to get as hh24:mi:ss and As mi.sec

to_char(to_date('1970-01-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss')+(column1.END_DATE_TIME-column2.START_DATE_TIME),'hh24:mi:ss') as TotalTimeTaken

  round(       
    (cast(EeMntrTxnHeaderEO.END_DATE_TIME as date) - cast(EeMntrTxnHeaderEO.START_DATE_TIME as date))       
    * 24 * 60      
  ,2) as TotalTimeTaken