The story
See by, sense 3: “not later than (the given time); not later than the end of (the given time interval)”.
Etymology from Wiktionary, CC BY-SA 4.0.
by now
Today it means: The hour being what it is; the hour being so advanced; considering that it is so far in time already; now that so much time has elapsed; if not before, now at the latest. Full definition →