The main cathedral and the archaeological area are open every day from 9:00 AM to 6:00 PM. Duomo Milan’s opening hours are the same every day. This means you can visit the beautiful interior of the cathedral, the crypt and the archaeological area beneath the cathedral.
The Duomo Museum is at Piazza del Duomo 12 inside the Royal Palace. It gives you a look into the history and art of the Duomo Milan. The museum is open from 10:00 AM to 6:00 PM every day except Wednesday when it is open longer until 7:00 PM. The last ticket is sold 50 minutes before closing time and the final entry is an hour before it closes. Remember that the museum is closed on Mondays so plan your visit for other days of the week.
How much time you need at the Duomo Milan depends on what you want to see. If you just visit the cathedral, the archaeological area, and the rooftops you will need at least two to three hours. If you want to explore more and include a visit to the Duomo Museum plan on spending three to four hours.