How to find out upto what time we can flashback our database

SET PAUSE ON
SET PAUSE 'Press Return to Continue'
SET PAGESIZE 60
SET LINESIZE 300
SET VERIFY OFF

COLUMN oldest_flash_scn FOR 999,999,999

ALTER SESSION
   SET nls_date_format='DD MON YYYY hh24:mi:ss'
/

SELECT
   oldest_flashback_scn,
   oldest_flashback_time
FROM
   v$flashback_database_log
/

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TIM

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           787294429 22 MAY 2017 06:35:11