Day trips from Zurich

How will you be travelling? By rail?
There are 90 minute circular boat tours leaving from the southern end of Zurich.
30 minutes from Zurich (by rail) is the beautiful small marina town of Rapperswil.
The town of Stans (check rail.ch/en for rail travel durations), with IT's mountain, the Stanserhorn, now featuring a topless cable car for the brave.
Of course, highly touristic Luzern is under one hour away as well. With IT's local mountain Pilatus.
Start researching! You can't go wrong!

Luzerne!! Or maybe Bern. Or maybe go to Interlaken, which is pretty far for a day trip but the train ride there would be beautiful.

Right now, you can each buy a Saver Day Pass for 61 CHF. That will give you unlimited travel in Switzerland for a day. Trains, boats, buses, trams. Here are a some suggestions.

Luzern, then a boat ride to Vitznau, then a train to the top of Mt Rigi, ride back to Vitznau and boat back to Luzern. the, if you still have time, you could do the previously mentioned Stanserhorn cable car. then back to Luzern and Zurich. All covered by a SDP.

Engelberg to visit the high Alps. Lifts will cost you extra in this case as they are not covered by the SDP.

Trip to Interlaken via Luzern to ride the scenic Interlalen-Luzern Express. You could also visit Wengen or Muerren. Lifts above thse towns will also cost extra as they are not covered by the SDP.

The price of the SDP increases over time as you get closer to your intended travel date, so buying early is a must. They are also nonrefundable,

https://www.sbb.ch/en/tickets-offers/tickets/day-passes/saver-day-pass.html

Lucerne would be on the top of my list. Also, the Lindt chocolate factory is about a half hour train ride away from Old Zurich. It's more of an afternoon trip than a daytrip though. You do need to book in advance. They also offer chocolate making classes.

You may also consider a day trip to Schaffhausen, an hours train ride from Zurich HB. It is a charming town on its own. Over there, you could visit IWC Schaffhausen watch museum. Watches are on sale as well for those who are interested. No need of any reservations for entry. In addition the spectacular Rhine Falls is a short local train ride away. These activities and a visit to the town centre could certainly make an enjoyable day trip.

I agree with others that Lucerne is maybe the best day trip from Zurich. If you are interested in micro nations you can also visit Vaduz, Liechtenstein easily from Zurich, which is something I quite enjoyed.

You only have a couple of days, so unless you (and your wife!) are really into watches, I would suggest spending most of your time visiting Luzern (more or less a must) and/or the mountain regions on day trips instead of going to Biel. If you want to fit watches in, you could follow the IWC Schaffhausen suggestion. It's a shorter train journey and you could also combine that with visiting the Rhine Falls and/or Stein am Rhein if those places interest you.
In Zurich itself, there is also the Beyer clock and watch museum https://www.beyer-ch.com/en/clock-and-watch-museum/
As for used watches, a lot of sales are online. But you could always check with one of the big watch shops on Bahnhofstrasse in Zurich (Bucherer or also Beyer), most of which offer certified pre-owned watches. Not really big bargains, but at least you know they are legit. Or you can just window shop :) There are also smaller resale shops like Galerie Inauen and Greenwich MT (you can google them) but I don't have first-hand experience to share.