Arequipa combines a colonial city center with one of the deepest canyons in the world nearby. Most travelers add it before or after Cusco, connected by flight. The real planning question is not whether the city is worth it, but whether your itinerary has room for the extra day or two that Colca Canyon needs.
If you only want the city, one day is usually enough for the Cathedral, Santa Catalina Monastery and a viewpoint like Yanahuara or Sabandia. If Colca Canyon is the reason you are considering Arequipa, plan for two to three days total — the canyon is not a side trip you can rush.
The condor viewpoint sits well above the city, and the road there takes hours each way. Most travelers stay overnight near the canyon rather than doing it as a single long day from Arequipa. [CONFIRMAR: operador, duracion exacta y precio del circuito Colca] before this is presented as a fixed itinerary.
Arequipa usually links to Cusco by flight, which keeps transfer time reasonable. It fits better in longer Peru itineraries — 10 days or more — where there is room to add it without competing with Machu Picchu logistics.