We - my son and I - had 23 hours in Zurich enroute to India from Florida last winter, so I can help :-) As we had to spend overnight by ourselves, we did not really have an option but to book a hotel. That said, we had finished our sightseeing whatever we could really do by about 6:30 pm (it started raining at about 4:45 pm - our worst case scenario, as there is only so much you can sightsee even with ponchos), so you could do everything we did. Just remember to have a plan B if the weather does not cooperate.
Our flight landed in Zurich about 10 am or so. Even though we were booked through to India, our bags were offloaded to us at Zurich as our halt was an overnight one. Never mind, I enquired around and though the first person we spoke with said that we could check the bags back in only the next day, I sought out another opinion, and a nice lady said that if we were on Swiss and leaving within 24 hours, we could check the bags right back which, needless to say, we did.
After purchasing the Zurich canton ZVV (after 9 am) pass from the SBB office in the same big airport terminal area, we were out of the airport by about noon. We then went to our hotel in Rumlang and left our carryon items there, then got to Uetliburg about 1:30pm or so. From there, we went to Rhine Falls reaching there at about 4:00 pm. Note that for your return, the last Winterthur-bound train stops at 4:15 pm or so in winter, so plan to walk back to Dachsen (we did - that was our plan B as I had not realized that the train does not stop that late in the afternoon!). It was dark by about 5 pm the day we were there - Christmas Day 2013. You should get at least 30-60 minutes more of daylight.
The next morning, it took us about 30 minutes from the time we were dropped off by the hotel's airport shuttle to get to our gate. Just to be on the safe side, I would plan on being there at least 2 hours before flight time.
For us, temps were in the high 30s low 40s. It snowed the day we were leaving ... but only after we reached our gate, so we could not spend time out in the snow.
PM me if you need more details. Of course, YMMV!!!
Porcupyn
PS: We had packed fingerfood so we did not spend any time for lunch/dinner.