This guide runs in both directions, and which one you are doing changes what you need from it.
Coffee first, then the train. Leave the café north-west. The market is about 509 metres and roughly seven minutes on foot by OpenStreetMap routing; the station is at that junction.
Off the train, then coffee. Reverse it. You come up at Bến Thành and walk south into the banking blocks, away from the market crowds. That leg is about 416 metres and roughly six minutes on foot by OpenStreetMap routing, to one entrance — the station opens onto the square at several, and the two map pins for it sit 125 metres apart.
What “one entrance” means here
The 416 metres above is a routing estimate to one entrance, not a claim about the whole station. Bến Thành is a city block with entrances all round the square, and they are not all the same distance from the café — the two authoritative map pins for the station sit 125 metres apart, which is why we say “an entrance” rather than “the entrance.”
So treat the figure as a reasonable one rather than a promise about the exact door you will come up through. The market leg above is the same kind of estimate — a routing engine’s number, not a walk any of us has taken with a phone in hand.
The first ten minutes above ground — which way you come up facing, and how to cross the square — are in Up the stairs at Bến Thành. The market at the same junction has a page of its own, and so does the station.