Using Flashback Query (SELECT AS OF) -link

To Set NLS_DATE_FORMAT
alter session set NLS_DATE_FORMAT='YYYY-MM-DD:HH24:MI:SS';
alter session set NLS_DATE_FORMAT='DD-MM-YYYY:HH:MI:SS';
alter session set NLS_DATE_FORMAT='YYYY-MM-DD:HH:MI:SS';

To select at specified time whit where  
SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Chung';

To find out the values has been modified 
SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
minus 
SELECT * FROM employees;

To find out the value what has been at 60 minutes ago
SELECT * FROM employees
AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)
MINUS
SELECT * FROM employees;

to Insert
INSERT INTO employees (
SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Chung');

INSERT INTO employees
(SELECT * FROM employees
AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)
MINUS
SELECT * FROM employees;