Yes, you can extend or shorten the duration of the Annapurna Circuit trek based on your preferences. The trek can be customized to suit your time constraints and fitness level. You can add side trips, rest days, or explore alternative routes to make the trek longer. Conversely, you can skip certain sections or use transportation options to shorten the trek if needed. It's important to plan your itinerary accordingly and make necessary arrangements in terms of accommodations and permits if you decide to extend or shorten the duration of the trek.