Riphekosh70
Years ago, return tickets were valid up to 10 days. But as there’s not necessarily a ticket control in every train, too much ticket abuse was happening by dishonest passengers using them multiple time on consecutive days. That’s the reason why return tickets are now only valid one calendar day (same for single point-to-point tickets). There’s no financial disadvantage for honest customers, as a return ticket is always twice the price of a single ticket.
So what you’ll need are two single point-to-point tickets. Uhm, without the Kloten city ticket upgrade, as the airport surroundings are really not that worth visiting, trust me.
Depending on how far the travel date is in the future, saver day passes might be a valid and cheaper option, however there’s no refund in case of a change of plans.
Just stay away from supersaver tickets after an incoming flight, as those are tied to the specific selected train(s) and there’s no refund in case of a flight delay.