Standard (point to point) tickets are for a route, not a train. So you can always take a later train. But Supersaver tickets are for a specific train. Do not buy those when coming of a flight.
What you should buy however is a Saver Day Pass. This is an “all you can eat” public transport pass good for the whole country. It will get you to Zermatt. Buy this here:
https://www.sbb.ch/en/tickets-offers/tickets/day-passes/saver-day-pass.html
This is going to be your cheapest option, and perfect when you arrive by air.
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