You could argue that the poem starts with the title, so it reads 'Archery was still a thing then.' I'm not aware of this being a named literary device.
The aspect of timing of an arrow may be a reference to Zeno's Paradox of the Arrow:
If everything when it occupies an equal space is at rest at that instant of time, and if that which is in locomotion is always occupying such a space at any moment, the flying arrow is therefore motionless at that instant of time and at the next instant of time but if both instants of time are taken as the same instant or continuous instant of time then it is in motion.
— as recounted by Aristotle, Physics VI:9, 239b5
In the arrow paradox, Zeno states that for motion to occur, an object must change the position which it occupies. He gives an example of an arrow in flight. He states that in any one (duration-less) instant of time, the arrow is neither moving to where it is, nor to where it is not. It cannot move to where it is not, because no time elapses for it to move there; it cannot move to where it is, because it is already there. In other words, at every instant of time there is no motion occurring. If everything is motionless at every instant, and time is entirely composed of instants, then motion is impossible.
Whereas the first two paradoxes divide space, this paradox starts by dividing time—and not into segments, but into points.
Or it may just literally be a reference to that lacuna you experience when you shoot an arrow, they move slower than bullets or projectiles in computer games and there is a brief moment of breath-holding after you loose the arrow while you wait to see where it lands. I've only ever shot at fixed targets, where timing is not a crucial thing, if you are shooting at a moving target, an animal or person you have to anticipate the space the target is moving into, so timing becomes more important.
That does itself flag up the potential for a crossover with Zeno's tortoise paradox, which says that a pursuer can never catch up with the pursued.
In the paradox of Achilles and the tortoise, Achilles is in a footrace with the tortoise. Achilles allows the tortoise a head start of 100 meters, for example. Suppose that each racer starts running at some constant speed, one faster than the other. After some finite time, Achilles will have run 100 meters, bringing him to the tortoise's starting point. During this time, the tortoise has run a much shorter distance, say 2 meters. It will then take Achilles some further time to run that distance, by which time the tortoise will have advanced farther; and then more time still to reach this third point, while the tortoise moves ahead. Thus, whenever Achilles arrives somewhere the tortoise has been, he still has some distance to go before he can even reach the tortoise.