What is the length of time it takes for a deleted Service Bus namespace to become available for another subscription.
I've deleted one and would like to recreate it in a different Subscription, however this is not working.
The duration of the operation is undefined. The documentation of the Delete Namespace REST API operation states:
This does not mean that the namespace is completely deleted at the return of the API call. It means that it is marked for deletion.
This forum thread ("Re-use namespace (azure)") contains information that the namespace name should be available in a few minutes for use in the same subscription, and that it is reserved for 7 days during which it can only be recreated in the original subscription. In case you can't wait, you may reach out to Azure support.
The Namespace Description REST API operation can be used to retrieve the namespace status (including "Deleting"). See also the NamespaceDescription.Status Property in the Service Bus Class Library for .NET.
The Check Namespace Availability REST API operation can be used to check when the namespace name becomes available after a delete request.