Even on a tight schedule, Florence Duomo (Cattedrale di Santa Maria del Fiore) earns the hours.
Allow 30–60 minutes (exterior + nave).
Keep the contrarian truth: after the long free-entry queue the nave is famously bare and anticlimactic, and the real value is the exterior, the dome climb and the Opera museum, not the inside. What the entry misses is the piazza as a living room, and it changes by the hour — at 8am it's near-empty, the marble going pink, locals cutting through to work; by 11 it's a tide of tour groups and selfie sticks; after dark it empties again and the floodlit façade is the city's best free spectacle. Treat the building as a thing to circle and photograph at the right hour, and the inside as optional.