Sep 6, 2019 - 8:47 PM
If it is going to be good weather in and around Luzern, I suggest taking the train to Luzern, hopping a boat to Vitznau, and then the train up to Mt. Rigi (2h 43min). Depending on your available time & energy, come down the same way, catch the next boat back towards Luzern, with perhaps a short stop in Weggis for a late lunch, then continue by boat back to Luzern and take the next train back to Zurich.
If you don't want to linger once at the top of Rigi, you can take the train down the other side to Arth-Goldau, then catch a train straight back to Zurich (1h 49min). Given your relatively late start from Zurich, this may be the better option. You can also get to Rigi by using this path in reverse.
We're planning on going to Liechtenstrein this October while we're in Zurich (1h 39min), but only for the "novelty" of it. And perhaps a brief stop at the Laderach Chocolate factory in Bilten on the way to or from Liechtenstein.