Yes, you can add the Park Hopper option to your Disney theme park ticket at any point during your visit, even in the middle of the afternoon. To do so, you can visit any ticket window, Guest Relations location, or use the My Disney Experience app. However, there is a major catch: the cost of the Park Hopper is a flat fee based on the total number of days on your ticket, not just the remaining days. If you are on day 3 of a 5-day ticket, you will still pay the same price as if you had added it on day 1. Once added, the benefit is applied to all remaining days of your ticket. Since early 2024, Disney has removed most time-of-day restrictions for hopping, so once you have the add-on, you can move between parks at any time during park hours, subject to capacity. Adding it later in the day is a great way to "save the day" if your primary park is too crowded or if you want to catch fireworks in a different park.