A major chemical company operates a private fleet of tank trucks that deliver full loads of liquid chemicals from warehouses to all associated customers. The “customers” in this case are plants using these chemicals within production processes that run 24 hours a day. If these plants run out of any of the necessary raw chemicals, they must shut down the ongoing production, which wastes precious time and costs them a lot of money. For this chemical company to fulfill the needs of these demanding customers, they need to offer no less than two-day service for all demand. The modeling team understands this policy but is puzzled about how they convert the service promise into a constraint within their network design model.