The due dates defined in Service Level Agreements are calculated based on the following elements:

Working calendar: This is a calendar that defines the working days and hours for a specific country or region. It also includes the public holidays and other non-working days for that location. The working calendar is used to determine the actual duration of a service level objective, excluding the non-working time12.

Operating hours: This is a time interval that defines the availability of a service team or an individual employee. It specifies the start and end time of the working hours for each day of the week. The operating hours are used to determine the actual response time of a service level objective, excluding the time when the service team or employee is not available3 .

The service contract and the maintenance plan are not elements that are used to calculate the due dates defined in Service Level Agreements. The service contract is an agreement between a service provider and a customer that defines the scope, terms, and conditions of the service delivery. The maintenance plan is a schedule that defines the frequency and type of maintenance activities for an installed base object.

References = 1: Working Calendar - SAP Online Help, 2: Configuring a Service Level Agreement - SAP Learning, 3: Operating Hours - SAP Online Help, : [Using Service Level Agreements - SAP Learning], : [Service Contract - SAP Online Help], : [Maintenance Plan - SAP Online Help]