A company's cloud-based single page application consolidates data local to the application with data from on premise and 3rd party systems. The diagram below typifies the application's combined use of synchronous and asynchronous calls.

The company wants to use the average response time of its application's user interface as a basis for certain alerts. For this purpose, the following occurs:
1. Log every call's start and finish date and time to a central analytics data store.
2. Compute response time uniformly as the difference between the start and finish date and time - A to H in the diagram.
Which computation represents the end-to-end response time from the user's perspective?