Oracle 11g Release 2

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ALTER SESSION SET NLS_TIMESTAMP_TZ_FORMAT = 'YYYY-MM-DD"T"HH24:MI:SS.FF3 TZR';
CREATE TABLE your_table ( timestampA, timestampB ) AS
SELECT TIMESTAMP '2019-09-25 07:00:00.000000000 +07:00', TIMESTAMP '2019-09-27 03:00:00.000000000 +04:00' FROM DUAL
1 rows affected

SELECT TimestampA,
       TimestampB,
       TRUNC( TimestampA ) - TRUNC( TimestampB ) AS days_difference
FROM   your_table


TIMESTAMPA
TIMESTAMPB
DAYS_DIFFERENCE


2019-09-25T07:00:00.000 +07:00
2019-09-27T03:00:00.000 +04:00
-2


SELECT TimestampA,
       TimestampB,
       TimestampA AT TIME ZONE 'UTC' AS utcA,
       TimestampB AT TIME ZONE 'UTC' AS utcB,
       TRUNC( TimestampA AT TIME ZONE 'UTC' ) - TRUNC( TimestampB AT TIME ZONE 'UTC' ) AS days_difference
FROM   your_table


TIMESTAMPA
TIMESTAMPB
UTCA
UTCB
DAYS_DIFFERENCE


2019-09-25T07:00:00.000 +07:00
2019-09-27T03:00:00.000 +04:00
2019-09-25T00:00:00.000 UTC
2019-09-26T23:00:00.000 UTC
-1