"Page Load time" is really not easy to define in general.
It depends on the browser you use, because different browsers may do more requests in parallel, because javascript has differents speeds in different browsers and because rendering time is different.
Therefore you can only really measure your true page load time using the browser you are interested in.
The end of the page load can also be difficult to define because there might be an Ajax request after everything is visible on the page. Does that count the the page load or not?
And last but not least the real page load time might not matter that much because the "perceived performance" is what matters. For the user what matters is when sHe has enough information to proceed
Markus
I'm not aware of any way (at least no I could tell you :] ) that would automatically measure your pages perceived load time.
Use AOL Pagetest for IE and YSlow for firefox (link see above) to get a "feeling" for you load time.