Yes, that’s perfectly doable.
Well, locals do buy Saver Day Passes and Supersaver tickets in advance, too. Tickets at normal fare, however, people here do not buy them in advance, perhaps earliest the day before travel. There is no financial benefit in buying them in advance, not even a guaranteed seat. Supersaver tickets must be bought in advance and are fine for travels where the price is more important than flexibility or a fast connection.
I had an Asian couple on the train the other day, they had a Supersaver ticket from Geneva to Interlaken Ost at 3 PM and found the city of Geneva too nice and therefore stayed until 5 PM. Then they took the train in the rush hour, with the ticket that was valid for the train at 3 PM. This was not going to work, they had to buy new tickets. Therefore, I say, with Supersaver tickets you sacrifice the flexibility. Nevertheless, if you want to go from A to B and the time and duration of travel is secondary, you are totally fine to use Supersaver tickets.
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