Oracle 18c

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create table table_a (create_time) as
select cast('08-MAR-19 08.23.47.897000000 PM GMT' as varchar2(50))
from dual;
1 rows affected

alter session set nls_timestamp_format = 'SYYYY-MM-DD HH24:MI:SS.FF3';
alter session set nls_timestamp_tz_format = 'SYYYY-MM-DD HH24:MI:SS.FF3 TZR';
select to_timestamp(replace(create_time, ' GMT', null),
  'DD-MON-YYYY HH.MI.SS.FF AM')
from table_a;

TO_TIMESTAMP(REPLACE(CREATE_TIME,'GMT',NULL),'DD-MON-YYYYHH.MI.SS.FFAM')

 0019-03-08 20:23:47.897

select to_timestamp(replace(create_time, ' GMT', null),
  'DD-MON-RR HH.MI.SS.FF AM', 'NLS_DATE_LANGUAGE=ENGLISH')
from table_a;

TO_TIMESTAMP(REPLACE(CREATE_TIME,'GMT',NULL),'DD-MON-RRHH.MI.SS.FFAM','NLS_DATE_LANGUAGE=ENGLISH')

 2019-03-08 20:23:47.897

insert into table_a (create_time)
select '10-MAR-19 10.11.12.123000000 AM America/New_York' from dual;
1 rows affected

select to_timestamp_tz(create_time, 'DD-MON-RR HH.MI.SS.FF AM TZR', 'NLS_DATE_LANGUAGE=ENGLISH')
from table_a;

TO_TIMESTAMP_TZ(CREATE_TIME,'DD-MON-RRHH.MI.SS.FFAMTZR','NLS_DATE_LANGUAGE=ENGLISH')

 2019-03-08 20:23:47.897 GMT

 2019-03-10 10:11:12.123 AMERICA/NEW_YORK

select cast(to_timestamp_tz(create_time, 'DD-MON-RR HH.MI.SS.FF AM TZR',
  'NLS_DATE_LANGUAGE=ENGLISH') as timestamp)
from table_a;

CAST(TO_TIMESTAMP_TZ(CREATE_TIME,'DD-MON-RRHH.MI.SS.FFAMTZR','NLS_DATE_LANGUAGE=ENGLISH')ASTIMESTAMP)

 2019-03-08 20:23:47.897

 2019-03-10 10:11:12.123

select cast(to_timestamp_tz(create_time, 'DD-MON-RR HH.MI.SS.FF AM TZR',
  'NLS_DATE_LANGUAGE=ENGLISH') at time zone 'Asia/Tokyo' as timestamp)
from table_a;

CAST(TO_TIMESTAMP_TZ(CREATE_TIME,'DD-MON-RRHH.MI.SS.FFAMTZR','NLS_DATE_LANGUAGE=ENGLISH')ATTIMEZONE'ASIA/TOKYO'ASTIMESTAMP)

 2019-03-09 05:23:47.897

 2019-03-10 23:11:12.123

select sys_extract_utc(to_timestamp_tz(create_time, 'DD-MON-RR HH.MI.SS.FF AM TZR',
  'NLS_DATE_LANGUAGE=ENGLISH'))
from table_a;

SYS_EXTRACT_UTC(TO_TIMESTAMP_TZ(CREATE_TIME,'DD-MON-RRHH.MI.SS.FFAMTZR','NLS_DATE_LANGUAGE=ENGLISH'))

 2019-03-08 20:23:47.897

 2019-03-10 14:11:12.123