The name came 101 years late
September 15, 1835. The Beagle reached the Galápagos. Some retellings walk Darwin ashore that day. The record keeps two dates: the ship reached the islands on the 15th; the anchor went down on the 16th, and his first hour ashore came then, at a spot now called Frigatebird Hill, on Chatham Island.
His first field note on a Galápagos bird wasn't one of the finches that carry his name. It was a mockingbird: “very tame & curious in these Islds. I certainly recognise S. America in ornithology.” He wrote down which island it came from. The finches he collected “not apparently with any single focus.”
The name took 101 years. “Darwin's finches” was first applied by Percy Lowe in 1936, fixed in place by David Lack's 1947 book. They aren't finches, either. They're tanagers.
He wrote, looking back: “it seems to be a little world within itself.”
The ship kept the 15th. The landing kept the 16th. The name came late, and it's still the wrong word.
Sources: Darwin Online, “Darwin's field notes on the Galapagos: 'A little world within itself'” (Galápagos Notebook pp. 18b, 30b; Journal of researches p. 454); Second voyage of HMS Beagle; “Darwin's finches” naming per Percy Lowe 1936 / David Lack 1947.