Oracle Database Discussions

I've got a couple of questions as it relates to the FLASHBACK_TIME and FLASHBACK_SCN parameters when using Data Pump for exports and imports.

First question...
If I didn't specify either of these parameters during the export is is still possible to use them during the import. For example, I started a data pump export of one of our databases at 4:30pm on June 25th. I didn't use either of those parameters during the export and it ran for 2 hours. There was a significant amount of activity in the database happenning during the export. Can I use the FLASHBACK_TIME parameter (setting it to 4:30pm on June 25) to get a consistent import of the database.


Second Question...
We take a nightly datapump export of the database using a job scheduled through cron. If I have to use FLASHBACK_TIME or FLASHBACK_SCN during the export in order to use it during the import, any suggestion as to how to generate a value for either of these parameters automatically so that the nightly job can continue to be run on a scheduled basis?

Any help would be greatly appreciated.