Why is HTTP Page Load Time lower than Hit Response Time?

How can HTTP Page Load Time be lower than Hit Response Time? Great Question!

The Page Load Time is the elapsed time between the first and the last hit of the page; thus, logically, it should be greater than the average Hit Response Time. Still, the page load time can sometimes be lower than the average hit response time.

The reason is that some hits aren’t accounted for in the page load time computation. It is, in fact, becoming more and more common to use AJAX calls to load portions of the page, and Skylight sensor: capture uses some heuristics to determine when the page has finished loading. This makes it so that some AJAX calls issued long after the page has loaded aren’t accounted for in the page load time computation. Yet they are hits of the page and their load times impact on the average hit response time.

Typically, when there are long AJAX calls after the page is loaded, the average hit response time may be greater that the page load time.

Asynchronous HITS after Page Load Time.