Wiktionary
late on
adv. at a late stage of something
Usage examples of "late on".
Henry, who was working late on long-delayed fee notes, told him that Soapy Sam was at a service with his peer group, the Lawyers As Christians Society, in the Temple Church.
W---- came on watch full twelve minutes late on this particular night,--a tremendous breach of etiquette.
It seemed that somewhat late on the afternoon of the day previous, while three of the stranger's boats were engaged with a shoal of whales, which had led them some four or five miles from the ship.