Suppose you have a Service Level Agreement to respond to customer inquiries within two business days.  A customer inquiry is submitted late Friday afternoon or evening.

The customer's case should not be past deadline by Monday morning.

A datetime property should be computed using the Calendar library setting the value to Monday morning. That property would be used for Assignment Ready. The work should be completed by end-of-day Tuesday.

In above example I would choose Dynamically defined on Property option in Assignment Ready. and Set the value of property from Calculate service level options. 
Please confirm if that;s correct. 

But in the example it says The customer's case should not be past deadline by Monday morning.

Then why The work should be completed by end-of-day Tuesday.

The Assignment does not start "clocking" until Monday morning because you configure it as Assignment Ready + Datetime property.   The value of the Datetime property is Monday morning.

The rest of the SLA is up to you, e.g., 1 day = Goal, 2 days = Deadline or use a Datetime property for the Goal and a different Datetime property for the Deadline.

If there is a 2 business day turn-around and work started Monday morning, the work should be completed by Tuesday night -- a full two business days.

Assignment Ready is also fair to those whose productivity is judged by how well they meet the Goal time and stay within the Deadline -- for example the Timeliness of Resolved Items By Operator report.

Great. Explanation.

Do you have any concrete example where I have to select Assignment Ready option is "Timed Delay"

Suppose you were to take an App Build exam by logging into a Cloud Instance. The exam officially starts Monday morning (your local time) at 10:00am say. You have 3 days to complete the exam. The exam assignment is pushed to your worklist at 8:00am. You are allowed to open the exam case from your My Cases view in review mode, look at the requirements for each question, and sketch out designs. You are also free to open the assignment and begin building the exam whenever you want. if you do this however, your score will be lowered because you did not fully utilize your allowed design "think time".   :- )
 

So in this Example Assignment Ready option will be "Timed Delay". In the Hours I will configure it to 2.

Calculate Service Level option will be "Interval from When assignment is ready" 

Since I have 3 days to complete the exam, I will configure 3 days in Goal.

Goal or Deadline does not matter. You develop the solutions on a laptop, not on the cloud instance. 

Optimistic locking would be used. The SLA would continue the flow after 3x24 = 72 hours have elapsed - nothing you can do to stop it.

Prior to the deadline would had to have attached everything you want to deliver such as solution zips, design documents, or test instructions. Videos tend to be overly large. A smaller, sped-up video perhaps.

This is all hypothetical of course, not how app builds are handled today.

Thanks, Pederson! Now, I have very good understanding about SLA...