Admin Assist FAQs: https://help.salesforce.com/articleView?id=000176637&type=1

See #8 When will my case be completed? Once you log your case, the assigned agent will assess the amount of work needed to complete the case and send you an estimated time of completion. For large requests (ex. record updates of 1mill+, updating 100 reports, etc.) it is recommended you log the case one week in advance.