I received photographs, texts and emails this morning showing that one of the fledglings had left the nest. It had gone down to scaffolding below the nest early in the morning.
I was spending the weekend and was able to get to the nest around 5 p.m. When I arrived I was surprised to see three eyasses in the nest. It turns out the fledgling decided it was too soon to leave and using the stairs of the fire escape returned to its two siblings. I guess this was extended "branching".
Urban nests continue to surprise me!