From a manufacturing perspective longer runs and larger batches are more efficient and less costly. However when too much product is made or bought then there is the risk of the product expiring. Therefore it is necessary to recalculate the lot size every time you make product. The lot size should be dynamic.
If the same equipment is used for making multiple products then each product in the campaign must be calculated to last the entire time of the campaign. The time of the campaign is the aggregate of all the time for making every product needed during that time plus the changeover time between the products.
This is one of the ways that a scheduling tool helps to balance the time constraints between shelf-life and manufacturing constraints.