FAQ:  I am trying to create a summary activity that is linked to the start of activity A (SS) and the finish of activity B (FF). To me this is a LOE or hammock activity type. 

They task types available are Short Hammock and Long Hammock. I am confused why there is a distinction, or two separate options. 

The help file indicates that the difference is the shortest duration vs the longest duration. In the example above, how can there be two different durations? 

Which Task Type should I be using?

When the Short or Long Hammock has only 2 logic links (linked SS to Activity A and FF to Activity B like in your example), the duration of the hammock will be the same whether you choose Short or Long.

The difference comes when the hammock has 3 or more logic links. The Short Hammock and Long Hammock tasks in the following example have the exact same predecessors but different duration, start, and finish.