Why are time-based deliveries sometimes not awarded an S rating even though delivery time was within the limit?

I've had several time-based deliveries that did not get an S rating, even though the delivery time was well under the specified limit. In these cases, I am playing on Hard difficulty and going for Premium Delivery.

In the past, I chalked it up to making partial deliveries for large cargo orders, thinking that to get the Premium award I needed to deliver it all at once. However, I just completed an order for the First Prepper, delivered all of the cargo in one trip and made it in 8:25 for a 35-minute limit. See attached photo.

There must be some qualification I missed, I just don't know what it was.

For time based deliveries, your rank depends on how fast you take to complete the delivery. For a 30 minute time limit, I believe it's sub-5 minute for S rank. It looks like you don't have the time in that yellow highlighting, so you definitely took too long.

You need to complete order in less than 20% (or 1/5) of order time limit. So to get S rating for 35 minute limit order you need to complete it in less than 7 minutes.

Cargo damage also affects results:

Scenarios for 25 minutes premium delivery (hard):

• Completed with 5:20 (0% damage) - RATED A
• Completed with 4:30 (9% damage) - RATED A
• Completed with 4:30 (6% damage) - RATED S

Source