Engine Odometer vs Total Engine Run Time when buying a truck?

Hey guys,

When buying a used truck, how much emphasis would you put on the total Engine run time, and how would you value idle time?

Example, I am looking at two trucks right now and here are their stats (other than stats mentioned, both are identical);

1. 2016 Freightliner Cascadia Evolution
Odo: 560,000 Miles
Engine Run Time: 18,000 Hours
Avg Speed: 31miles/hour (Assuming cruise speed of 62mph, this truck idles 50% of the time)
Price: $48,000

2. 2016 Freightliner Cascadia Evolution
Odo: 480,000 Miles
Engine Run Time: 10,000 Hours
Avg Speed: 48miles/hour (Assuming cruise speed of 62mph, this truck idles 33% of the time)
Price: $65,000

What is this lesser idle time worth if anything when making a purchase?

Secondary question: How do you test health of the after treatment system, for engine I understand you can test oil sample, blow by, compression test, and dyno. Are there any tests you can do before purchasing to similarly diagnose the after treatment system?

Thank you

 

Both trucks are from same company, they ran usually from Toronto, ON to Greater Chicago Area.

I understand there can be major variations, I am mostly interested in the general question; How do you value idle time, given similar circumstances and how do you test the after treatment system pre-purchase to see if the increased idle time has negatively affected the systems.

 

After the feedback on my first post I've actually decided to hold off on buying the truck for now, just browsing, seeing what's on the market and trying to figure out how to diagnose after treatment system prior to purchase.

I suppose your suggestion would be to look for a o/o upgrading or getting out of the business? If so, I am looking for that elusive o/o.