What is the purpose of Lineage Duration in View Data Provenance

Hello 
We have a pretty big flow in NiFi (NiFi 2.8.0) having many processors and my requirement is to determine how much time a particular request took. Most of the request starts with a HandleHttpRequest Processor and has some 250 processors in between them (some in the same process group and some in different process group communicating through Input and Output Ports).

Sometimes we notice the request to be taking 1 minute to return the response and sometimes as less as 10 sec.

So want to diagnose what is taking time.

How do I determine this?

I went to View Data provenance of a particular processor and then View Details and there in Details section I see some properties like-- Time, Event Duration and Lineage Duration (it is showing <1 sec for both these last two fields ). So I am not able to check accurate as it shows less than symbol. 
Which of these will represent the total time it took end to end (HandleHttpRequest to HandleHttpResponse). Also any rules which processor I need to do view data provenance for this or I can select any random processor in between. 

What is the purpose of “Show Lineage”? When I click this, it shows symbols of many processors connected. While for small process groups like having say 5 processors, I see all of them but for my large app which had 250 processors I am not able to understand this. Does it show only some processors depending on where I clicked?