There have been a number of requests around extending the Delegation functionality to inclue Start & End/Expiry Dates, as well as some method to trigger it outside of the Delegation Setup page. These could be addressed by adding the Activate Delegation checkbox field as a field that can be updated against a Person using the Manage CMDB task in a Workflow. If that is done, then workflows can be created to check this checkbox on the Start Date, delay until the End/Expiry Date, and then unchecked this checkbox. You could also provide confirmation emails to the Person at each stage of the process.