Multiple commitments occur when several operations are scheduled to start or finish at the same time on a work center. This can happen for different reasons, depending on the settings of the strategy profile and the work center. Two possible reasons are:
The Finite Scheduling indicator is NOT set in the strategy profile. This means that the system does not consider the capacity availability of the work center when scheduling the operations. The system only checks the basic dates and the relationships between the operations. Therefore, the system can schedule multiple operations at the same time on the same work center, resulting in multiple commitments.
The work center has several individual capacities. This means that the work center can perform several operations simultaneously, depending on the number and type of individual capacities. The system assigns the operations to the individual capacities based on the capacity category and the priority.
However, if the individual capacities have the same capacity category and priority, the system can assign multiple operations to the same individual capacity, resulting in multiple commitments.
References: Scheduling | SAP Help Portal, Strategy Profile | SAP Help Portal, Individual Capacities | SAP Help Portal.

You can limit the validity of a BOM by plant and by period. The plant determines the organizational area of validity for the BOM, and you can assign the same BOM to different or further plants if the prerequisites are met. The period of validity for a BOM is restricted by the valid-from date and the valid-to date in the BOM header and item, which determine when the BOM becomes effective and when it ends. References: Validity of Bills of Material, BOM Item Validity

The duration of an operation for production is determined by the combination of data maintained in the routing and the work center. The routing defines the sequence of operations, the work centers, and the standard values for each operation, such as setup time, processing time, and teardown time. The work center defines the capacity, the formulas, and the scheduling parameters for each operation, such as base quantity, operation rate, and queue time. The system calculates the duration of an operation by multiplying the standard values from the routing by the factors from the work center formulas and adding the scheduling parameters from the work center. For example, if the routing specifies a processing time of 10 minutes per unit and the work center formula is processing time = (processing time / base quantity) * operation quantity, and the base quantity is
100 units, then the duration of the operation for 50 units is (10 / 100) * 50 = 5 minutes.
The bill of material (BOM) and the material master (D) are not data objects that determine the duration of an operation for production. The BOM defines the components and the quantities that are required for producing a material. The material master defines the general and specific attributes of a material, such as the material type, the unit of measure,the MRP data, and the production data. These data objects are relevant for planning the material requirements and the production costs, but not the operation duration. References:
https://help.sap.com/docs/SAP_S4HANA_ON-PREMISE/c00ad2cac7be4ef29a4461ba114e4f91/051ebf53d25ab
https://learning.sap.com/learning-journeys/manage-production-orders-in-sap-s-4hana-manufacturing/scheduling-

The planning strategy Finite Scheduling with Reverse allows you to schedule production orders backwards from the requested delivery date, taking into account the available capacity and material constraints. To allow scheduling the past, you need to specify a negative offset time in the strategy profile. The offset time defines how far in the past the system can schedule the production order start date. For example, if you specify an offset time of -5 days, the system can schedule the production order start date up to 5 days before the current date. This can help you to avoid late deliveries and reduce lead times.
References: [SAP S/4HANA Production Planning and Manufacturing Certification Guide], page 97; [SAP Help Portal: Finite Scheduling with Reverse]