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In the ZVV fare network, a single journey ticket is valid 1 or 2 hours, depending on the number of included zones. For ZRH airport to the city, it‘s only 1h.
A twice as expensive return journey ticket is valid 24h, there‘s nothing in between.
There‘s no point buying first a single ticket Airport - City for 7.00 and then a Zone 110 (= Zurich City) Return/24h ticket for 9.20 (even if you don’t return the airport), as this would be more expensive than the zone 121/110 24h ticket for 14.00.
On the apps and ticket webshops, the symbols for single (1-2h) vs. return (24h) tickets on the respective buttons are a single arrow vs. 2 arrows. Single tickets are usually half the price of a return ticket.