I just posted about this. For May 23 it shows sold out for me for 6 pm (only time option offered). Isn't the fireworks at like 9pm?
i think when they originally post the reservations (usually 180 days out), park hours may not be solidified or properly entered into the system, so they just put a random time in. This happened to me last time too, wishes was at 8, but the reservation time was 6:20. They started letting people in a little before 7 and started serving at 7.