Correct me if I'm wrong, but you cannot move a folder with its containing documents without moving those same documents first.
Furthermore since SPD does not let you loop, you could not accomplish this task using it.
In order to accomplish this with the assumption that there may be documents within those folders, you could create a Visual Studio Coded Workflow to attach to your list.
For this purposes of this explanation I will assume you will not have nested folders...
- Pause for 30 days
- Add an 'if' block to check if the current item is a folder
- Create a folder with the same name as current item in the target document library
- Loop through all items contained within this folder
- Copy Document to target document library folder
- Delete Document in current folder
- Delete current item
If you want to go this route and need code samples, let me know and I would be happy to supply.