This feature is not available in Openx. By installing this mod you can have this feature  

• This mod will be working for all versions of Openx. This mod allows toggling banners using single invocation code.
•  In openx (or any other adserver), invocation code will display only one banner, but using this mod, you can server double banners to user.
• This mod will create new invocation code which publisher need to paste in his page.
• Now when page will be requested by user one banner will display and after some seconds invocation code will change that banners automatically.
•  So, two banners will be served to user (advantage for Advertiser) so that probability will be increase of clicking on users (advantage for publisher and you).
•  If you want to set the time of displaying banner then please see the mod "Admin Control Toggle Banner".
• Also, you can set time of toggling. 

SPECIAL FEATURES:

• Using this mod you can link two banners to same zone.
• This mod is very useful to the administrator, advertiser and the publisher.
•  It is user friendly and easy to install.