To check at what point the system is responsive enough to launch a browser. So, not just calculating the boot times (we have that already), but from power on to launching a browser.
While that's not an entirely unreasonable idea, I note that launching a browser has its own startup time. Power on to opening a document in evince is faster than power on to launching a browser, and that's support for the original thesis in a way, but it also feels like a little much to count it against "boot time".
Why? By the time you're logging in, booting is already finished.