It has been confirmed
What if the return time for that selection is not until much later in the day?
Walt Disney World has confirmed that guests will be able to make another reservation 120 minutes after their first reservation even if they have not yet redeemed the first
Genie+ selection.
In practice, this means that you might make a reservation at 7:05 am for Splash Mountain that has a return time of 10:00 am. At 9:05 am–before riding Splash Mountain, you’d be able to make another ride reservation.