You can get return times as soon as you enter the park, but you can't get a return time for any attraction that isn't officially open and you can't get return times for any attraction before the official early entry time. Say the early entry time is 8:30am but they allow you to enter the park at 8:20 am, you can get return times for shows, but not rides at that point in time. As soon as 8:30 hits you can get return times for attractions that are officially open for early entry. So if at Animal Kingdom, you can get a return time for Flights of Passage at 8:30 AM, but because Kilimanjaro Safaris isn't officially open for early entry, you can't get one for that attraction, even though it usually opens for early entry.