Help in utilizing workstations and operations

I am trying to wrap my head around setting up our work stations and operations.

Use Case:
Manufacturing sterilized grain bags.

I have a BOM of 5lb grain bag with an operation of ‘fill bag’ that is based on time it takes to fill one bag. But then I need an operation of ‘sterilize’ that utilizes multiple bags in the process, but the time it takes is always the same no mater how many bags are running through the operation.