How can I understand the "asyncTime" in TodoMVC benchmark test?

Question

I wanted to do performance benckmark test among my javascript framework and other frameworks.And I found the "TodoMVC" benchmark test.A lot of people use the result of this test.It seems reasonable.But I can't understand the "asyncTime" of this test.

var startTime = now();
testFunction(prepareReturnValue, contentWindow, contentDocument);
var endTime = now();
var syncTime = endTime - startTime;

var startTime = now();
setTimeout(function () {
    setTimeout(function () {
        var endTime = now();
        callback(syncTime, endTime - startTime);
    }, 0)
}, 0);

This is the code snippet to get "syncTime" and "asyncTime".

Why does it use two "setTimeout" to get "asyncTime"?

Dose it make sense?

This is the original repository. https://github.com/Matt-Esch/mercury-perf