Originally Posted by
KLouis
Doable. Assuming no delays coming in, you'll be able to take a train to the Hauptbahnhof around 11 and you'll have to take one back to the airport around 1:30. That leaves you with two hours strolling through the city centre and the lake and grabbing some street food. As for your other questions, a) nothing really interesting to do around the airport and b) Swiss immigration is super-efficient (especially when compared with the US).
Street food? There's not so much in Zürich. However, at the airport, just before you get to the bus terminal, there is a small version of Sternen Grill, where you can get a pretty descent St. Galler bratwurst.
But, me, I'd take the train to Stadlehofen and grab your bratwurst near the lake at the main Sternen Grill, then walk slowly back to the HB along Bahnhofstrasse and then take your train back to the airport and arrive around 13:30. Or just take the train back from Stadelhofen. Price is the same. If you're not in the pointy end of the airplane to KOS, and maybe even if you are, grab a nice dessert at Sprüngli in the main terminal when you're airside, but make sure there isn't a big line downstairs for passports. It's unusual, but it happens.
https://www.sternengrill.ch