Three days is the length that makes Zurich feel finished rather than sampled. Less, and you only see the station. More, and you should add a mountain only if the sky is actually clear.
Day 1 — land and the water
Zurich Airport to the hotel, then nothing heroic: the lake, a short Old Town walk, an early dinner. Fight the urge to shop while you are still on Gulf time.
Day 2 — the city properly
Lindenhof, the two churches if you want them, Bahnhofstrasse with appointments if watches or jewellery are the point. This is the day a private guide earns the fare.
Day 3 — out and back
Lucerne if you want a town and a lake with mountains on it. Rhine Falls if you want a shorter, louder morning and an afternoon free in Zurich. Not both. Fly the same evening only if the flight is late; ZRH is close but not magic.
Send the arrival time and who is travelling. We will put the three days on one sheet, in Arabic.