This is currently not possible as only deployments can be scheduled. This scenario requires the edit of the OU (linking to the GPO) to be scheduled as well as the changes of the OU (Deployment) be scheduled.
The GPO can be deployed to the Live Environment, the GPO linked to the OU and then the OU deployment scheduled. As the GPO is deployed before hand, the link to the OU can be established in GPOAdmin and deployment of the change to the OU scheduled. The GPO is deployed without any Scope of Management (SOM), so there should be no impact on the intended objects as the Scope has not been deployed until the OU changes are deployed.
Enhancement request TF00684331 has been submitted to Development for consideration of having the ability to Schedule Edits in a future release of GPOAdmin.