Trains from Zurich to St Moritz

Hi
Am flying into Zurich around 6am and then going to St Moritz by train. Am unsure whether to prebook train or not as we don't exactly know what time we'll be getting to central station, after we get thru the airport etc etc.

I'm happy to wing it - but want to know if that's wise? If we can't get on one train coz it's full, would we be generally speaking ok to get on the next one? It is a Saturday in early July that we'll be arriving. I've been told by local swiss travel info provider that I cannot book a ticket then change it, I'm not sure if that's actually the case or not.

Thanks

In Switzerland train tickets are not for a special train they are for the rout.
So you can buy a ticket and then you have to reach your destination at the same day.
You along you rout you can make so many stops you want.

Reservation is not needed not even possible.

Zürich Airport has it's own train station

There are two connections per from the airport to St Moritz per hour.
They starts xx:13 and xx:43 from the airport station.
When you take the xx:13 connection you will have a dinning car
for nice breakfast in the train between Zürich and Chur.
When you take the 10:13 connection you have a dinning car between Chur and
St Moritz for lunch.

The last connection starts at 20:13 reach St Moriz at 23:48.
You see you have enough time for plane delays emigration problems and last
luggage.
But one hour is a realistic time get from the gate to the Airport train station.
More infos about the train you get at SBB .

Don't worry. Nobody prebooks train seats in Switzerland. Follow the railway signs in the airport and you will arrive at the counters of the Zurich airport railway station. Buy there your ticket, half fare card, Swiss Pass, family card (free) or what ever you need and board the next train to Zurich HB (main station). 10 minutes ride, about 10 trains every hour.
Timetable from Zurich HB:
Zurich HB dp 7.07 and 8.07 - St. Moritz ar 10.19 and 11.19, change at Landquart
Zurich HB dp 7.37 and 8.37 - St. Moritz ar 10.58 and 11.58, change at Chur
Standard tickets of Swiss railways are valid the whole day, for any train; you can take the train you like, hop on and hop off as many times as you like.

If the weather is fine, there will be many people on a Saturday morning. But don't worry: board the train at Zurich HB at least 10 min prior to the departure (free seats in second class rather at the head end of the platform, about 300 metres away from the arrival hall) and you will be fine. Furthermore, once in the railway station, check if there will be a relieve train starting about 2 min earlier than the sheduled train.

Ditto, no problem, no reservation required and frequent trains.