The amount of time visitors spend inside Buckingham Palace can vary depending on their interests and the activities they choose to participate in.
If you're interested in touring the State Rooms, it's recommended to allow at least two hours for your visit. This will give you enough time to explore the State Rooms, which feature historic artworks, furnishings, and other treasures, and learn about their rich history through the audio guides provided.
If you're also interested in visiting the palace gardens, then you may want to allocate an additional hour or two to your visit, especially if you plan to take a leisurely stroll and enjoy the scenery.