It's not _that_ bad. It's a nice city and all. I bet you'd even have a pretty fun time in Zürich. After all, those of us who live in the area seem to like it. But with places like Luzern and Bern just an hour away, it's nicer to go to those places.

BTW, if you're in Zürich on a Sunday it is pretty much all closed up, but so is most of the rest of Switzerland.

Of course, given your short time, 4:30pm-12:30pm the next day. By the time you'd get out of the airport and all, you're probably at 5pm in Zurich, or 6pm or so in Luzern. Then, checking into a hotel, so a bit more time.... You would have time for a nice walk by the lake in either place. And, then depending on what sort of dinner you'd want, you can either sit down to a nice meal, or just grab something quick.