FLASHBACK INSTEAD OF DELAYING APPLYING OF LOGS ON STANDBY:
If you have multiple standby sites, you may utilize the DELAY option in Data Guard to prevent physical/logical corruption or user errors in your primary database.
For example If your primary database has only one standby database , a logical or physical corruption in the primary database will cause an immediate corruption in the standby database.
To avoid such a pitfall, you can implement the ‘Delay’ option (introducing a delay of minutes or hours on the second standby database for applying archive log changes).
This will prevent the corruptions on the second standby database and allow recovery from a possible physical/logical corruption or user errors in the primary database.
You can issue the following command to accomplish this:
SQL> alter database recover managed standby database delay 60 disconnect;
Using Flashback Database in a Standby Database Configuration
However, in Oracle 10g, you can configure the standby database with Flashback Database to achieve the same benefit as the DELAY option.
Therefore, there is no need to implement a second standby database with the DELAY option.
On primary at 10 a.m a corruption occurs which is propagated immediately to the standby database.
At this point you can FLASHBACK the primary database to a time just before 10 a.m. and then flashback the standby as well so all data is recovered up until the point of corruption.
Example in document below.