July 28th: Well, that didn't take long at all. After only 9-10 days the fledglings had vacated the nest and were perched on a branch a few feet above.
They continued to call out to their parents for food. ...Mom and Pop didn't waste any time getting back to business, however -- for within days of the fledglings' departure, one of them was back on the nest, with the other (the male, I think) building it up with more twigs.
Now there's one parent sitting on a new clutch of eggs and the other looking after the first set of fledglings. (Perhaps this makes up for the fact that other songbirds raise twice as many chicks in a brood.)