MERGE INTO ITM_INTFC_EV a USING
  (SELECT 1 ITM_EV_SEQ_NBR,
            'EAGAN' ITM_EV_SERVR_SITE_CD,
                    'IDA' EV_RCVR_CD,
                          'MSG' MSG_TYPE_CD
   FROM DUAL) b ON (a.ITM_EV_SEQ_NBR= b.ITM_EV_SEQ_NBR
                    AND a.ITM_EV_SERVR_SITE_CD= b.ITM_EV_SERVR_SITE_CD
                    AND a.EV_RCVR_CD= b.EV_RCVR_CD
                    AND a.MSG_TYPE_CD= b.MSG_TYPE_CD) WHEN MATCHED THEN
UPDATE
SET a.INTFC_EXPRT_IND='N' ,
                      a.SYNCH_STS_CD='1' ,
                                     a.UPDT_USER_ID='1' ,
                                                    a.UPDT_USER_SITE_ID='1' ,
                                                                        a.LAST_UPDT_LCL_DTM=sysdate ,
                                                                        a.LAST_UPDT_UTC_DTM=sysdate
WHERE a.LAST_UPDT_UTC_DTM<=sysdate WHEN NOT MATCHED THEN
  INSERT (a.ITM_EV_SEQ_NBR,
          a.ITM_EV_SERVR_SITE_CD,
          a.EV_RCVR_CD,
          a.MSG_TYPE_CD,
          a.INTFC_EXPRT_IND,
          a.SYNCH_STS_CD,
          a.UPDT_USER_ID,
          a.UPDT_USER_SITE_ID,
          a.LAST_UPDT_LCL_DTM,
          a.LAST_UPDT_UTC_DTM)
  VALUES (1 ,
          'EAGAN' ,
          'IDA' ,
          'MSG' ,
          'N' ,
          '1' ,
          '1' ,
          '1' ,
          sysdate ,
          sysdate);

----------------------------------------------------------------------------------------------------------
| Id  | Operation                 | Name         | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
----------------------------------------------------------------------------------------------------------
|   0 | MERGE STATEMENT           |              |     1 |    90 |   157   (2)| 00:00:03 |       |       |
|   1 |  MERGE                    | ITM_INTFC_EV |       |       |            |          |       |       |
|   2 |   VIEW                    |              |       |       |            |          |       |       |
|   3 |    NESTED LOOPS OUTER     |              |     1 |    77 |   157   (2)| 00:00:03 |       |       |
|   4 |     FAST DUAL             |              |     1 |       |     3   (0)| 00:00:01 |       |       |
|   5 |     PARTITION RANGE ALL   |              |     1 |    77 |   154   (2)| 00:00:03 |     1 |   290 |
|   6 |      PARTITION LIST SINGLE|              |     1 |    77 |   154   (2)| 00:00:03 |   KEY |   KEY |
|*  7 |       TABLE ACCESS FULL   | ITM_INTFC_EV |     1 |    77 |   154   (2)| 00:00:03 |   KEY |   KEY |
----------------------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   7 - filter("A"."ITM_EV_SEQ_NBR"(+)=1 AND "A"."MSG_TYPE_CD"(+)='MSG' AND
              "A"."EV_RCVR_CD"(+)='IDA' AND "A"."ITM_EV_SERVR_SITE_CD"(+)='EAGAN')

INDEX_NAME	COLUMN_NAME
ITM_INTFC_EV_MSG_IDX	MSG_UTC_DTM
ITM_INTFC_EV_MV_IDX	INTFC_EXPRT_IND
ITM_INTFC_EV_MV_IDX	LAST_UPDT_UTC_DTM
ITM_INTFC_EV_SYNCH_IDX	SYNCH_STS_CD

Thanks John I will create index on those 4 columns and  will
try again.
I am just surprised that it is showing 3 secs execution time
in execution plan