By default tickets are for a route, not a train. So even though you select a train from a schedule when buying a ticket this does not imply that this ticket is for that particular train.
So you intend buy a ticket Zurich Airport to st. Moritz for a particular day, When you do that you will see two or three options.
- The first open is a so called “Point to Point” ticket. That is valid for a whole calendar day, till 5 the next morning. And allows you to make one trip on the route you bought the ticket for. So you can just hop on the first train after you get out of arrivals. Such tickets are always available, even minutes before departure.
Note that there are two routes to St. Moritz. Either via Chur, or via Landquart. A normal Point to Point ticket is valid via either.
- The second option offered if you buy this ticket a few days in advance is a “Supersaver” Ticket. Such a ticket is discounted, but not flexible. With this ticket you indeed must take the trains you selected. Buying such a ticket is not advisable when arriving by air.
- Often you will get a third option, especially when you book far in advance: A Saver Day Pass. This is a discounted day pass, that gives you a whole day of unlimited travel on the entire Swiss Public Transit Network. Yes, all of it. Every train, tram or bus. These passes however are limited in availability, and the price increases the closer you are to the travel date. However if a pass is available at a price below the Point to Point ticket it will be offered to you when buying tickets. This Saver Day Pass is a very good option to get in connection with a flight, as it is fully flexible, and discounted.
So basicallly my advise: As soon as you have booked your flight, go to sbb-tickets.cc and and see if a Saver Day Pass is offered when you try to book ZRH to st. Mortiz. When it is, buy it.
Otherwise, just wait till you are at the airport and get a normal, point to point ticket.