The number of End User Business Hours for Auto Close functionality is calculated based on a Workshift assigned to a Requester. If the Affected End User and the Requester of a ticket are different, the Requester's Workshift will be used for the Auto Close calculations. If the Requester does not have the Workshift, the default Workshift, "Regular", will be used.
If the Time Zone is set to the Requester, the calculation will be done based on the Time Zone. If it is not specified, a server's system time where Service Desk Manager is running on will be used.