The park is open for Extra Magic Hours or Early Park Admission, but my plan does not use them

First, if your plan is for Walt Disney World in Florida, are you sure that the park offers Extra Magic Hours on the date in question? Disney has a similar sounding (but substantially different) event called Early Morning Magic, and it's easy to confuse the two.

Beyond that, note that not all attractions are open for Extra Magic Hours at Disney Parks or Early Park Admission at Universal parks. At Walt Disney World, more attractions are open during Evening Extra Magic Hours than during Morning Extra Magic Hours.

At Disneyland Park and Magic Kingdom, normally just Fantasyland and Tomorrowland attractions are open during the Morning Extra Magic Hours. This confuses up people who, for example, want to ride Big Thunder Mountain during that time.

At Universal Orlando, only the Harry Potter-related rides are consistently open, plus one or two other rides. Other attractions may be added during busy periods, but it's tough to predict that.

The most common example is that someone is trying to experience attractions in Magic Kingdom's Adventureland and Frontierland (Big Thunder, Splash, Pirates, etc.) during an 8:00-9:00 AM Extra Magic Hours on a day that the park opens to the public at 9:00 AM. If your plan has no attractions in Fantasyland or Tomorrowland, it'll show free time until around 9:00 AM, even if your plan has use of Morning Extra Magic Hours enabled. In that case, add some Morning EMH attractions to your plan, or else there's little point in showing up for Morning EMH.