I'm currently trying to create a developer sandbox. There is only one other sandbox used in our org (and it has a a status of Complete) and no other sandboxes ahead of it being created. Why is this in queue?
Queue doesn't mean in your particular org. Salesforce has put this in queue for all the other requests they have across all the orgs. This queue time can vary. Sometimes its 10 minutes, sometimes is hours.
https://help.salesforce.com/apex/HTViewSolution?id=000204612&language=en_US