How do you measure the "OTD" for EX-Work shipments?

Is an On Time Delivery OTD metric taken on any given date measured by what has shipped on that date only (whether the shippments were late or on time) ? i.e. Shipped 10 orders on a date. Of those 10 orders, 1 was late and 9 were on time - 90% OTD or Is an On Time Delivery OTD metric taken on any given date measured by what has shipped on that date vs. what was due on that date ? i.e. 10 Orders were shipped on a date, 1 of those was late, however, 10 other orders were also due but not shipped - 45% OTD

First of all , Ex-work mean shipment collection to be arranged by the customer by his nominated freight forwarder.it solely becomes the responsibility of the customer. 

In such cases,  note down the shipment collection in the last six months. Pen down the no of days taken by each customer for collecting the shipment with EX-WORK price base

Accordingly set the KPI for OTD (on time Delivery)  based on the no of day  required from the time of order receipt to the time of collection.