Lunch and dinner is the same. I was able to get a Fantasmic package for 4pm. They probably just don't have any available right now for the day you are looking at.
OP, I noticed that too when we booked the package. We just booked a lunch time. I just checked a few other dates in Sept and the beginning of Oct and they were only showing lunch times too. That's weird. Maybe it's bc Mama Melrose is the most popular restaurant offered in the package and it's all booked up already , idk. Maybe someone else who knows for sure will chime in.
My CSR said to call back - we have a 4:30 too - they told me to call back because later times were not available yet. I couldn't make ADRs online because the system wasn't working on my 180 day.
The dining package is for the first show only. If the first (or only) show is at 8:30, they will offer later reservations for the F!DP compared to when the first (or only) show is at 6:30.
Yesterday I was able to book F! at MM on 9/24 @ 4:50.
However, I am not sure if I want to keep the ADR or if I want to just do stand by for F! and dine at Sci - Fi. Since it is Sept it should not be a busy time in the parks.