The duration of sightseeing tours in Bilbao can vary. Shorter tours, such as 'Explore the Beauty of Bilbao by Foot', may last a few hours, offering a succinct yet enriching experience. More comprehensive tours, like 'Bilbao's Grandeur: A Historical & Architectural Walk', can span several hours to a full day, allowing for a deep dive into the city's architectural wonders and historical contexts. The length of the tour typically correlates with the depth and breadth of content covered.