Back to the original question
I found out yesterday, when I lost my internet connection in the middle of a load, that it's when you see the quote appear. All that black space before it loads doesn't count. But, once a partial page comes up, it's going, even though you can't type yet.
As for when it ends, I think it's when the stats page comes up. I've had some fairly quick solves that came up with longer times than I thought. Must be processing time.
And, for the record, I'm on Safari.
Slotted spoons don't hold much soup. - Stephen Sondheim