A multiple bill of material (BOM) is a type of BOM that allows for different combinations ofcomponents or raw materials for the same assembly or subassembly. The reason for different combinations of components in a multiple BOM could be the manufacturing date or the lot size. The manufacturing date determines the validity period of the BOM, which means that different BOMs can be valid for different time intervals. For example, a BOM can be changed due to a design modification or a change in the availability of components.
The lot size determines the quantity-dependent explosion of the BOM, which means that different BOMs can be used for different production quantities. For example, a BOM can be optimized for different batch sizes or different production methods. References: Multiple BOM, BOM Explosion

When you create a product master in SAP S/4HANA, you need to enter values for mandatory fields such as product number, product type, base unit of measure, and description. The product type determines the category of the product, such as material, service, or article. The base unit of measure defines the unit in which you manage the product in all business transactions. The selection screen for views and plants are optional fields that allow you to choose which views and plants you want to maintain for the product master. References: Creating Products, Understanding the Concept of Master Data

Lead time scheduling is a method of scheduling production orders that calculates the start and finish dates of each operation based on the operation duration, interoperation time, and other time elements. The time elements that are relevant for lead time scheduling of a production order are:
Setup time: The time required to prepare the work center for the operation, such as changing tools, adjusting machines, or cleaning the work area.
Processing time: The time required to perform the operation, such as machining, assembling, or testing the product.
Teardown time: The time required to restore the work center to its original state after the operation, such as removing tools, resetting machines, or disposing of waste.
Interoperation time: The time between two consecutive operations, such as transportation, waiting, or inspection time.
Float before production: The time buffer before the scheduled start date of the production order, which can be used to compensate for delays or changes in the production plan.
Float after production: The time buffer after the scheduled finish date of the production order, which can be used to compensate for delays or changes in the production plan.
The opening period and the total replenishment lead time are not relevant for lead time scheduling of a production order. The opening period is a parameter that defines the earliest possible start date of a production order, based on the material availability date and the planning time fence. The total replenishment lead time is a parameter that defines the total time required to procure or produce a material, from the time the requirement is identified until the time the material is available for use.
References: [Production Planning with SAP S/4HANA], pages 177-179; [SAP Help Portal: Lead Time Scheduling].