Problems with open period

I tried Open Period.

The concurren program said on log file the follow message:

There are not enough period defined in your Calendar. Please define your future enterable periods

I found the DOC ID 1383731.1 and it said

To resolve the issue

Please make sure that the effective As-of Date in the Manage accounting Periods UI is pointing at the period prior to the one that needs to be opened, before cliking on the Open Next Period button

The question is where in the application I can see effective As-of_date ?

Thanks and Regards