Hi Yuka!
Welcome to planDisney.
You have planned a lovely day!
I think you might
just make it to your dining reservation, but let's talk it through -
Happily Ever After lasts for around 18 minutes. Most guests will exit Magic Kingdom Park immediately afterwards, creating long queues at the bus stops. However, if you watch the fireworks from close to the park entrance on Main Street USA you might stand a good chance of exiting the park quickly. As a bonus, I have heard that the projections on the buildings of Main Street USA give you some of the best viewing experiences, that you'll miss if you are closer to Cinderella Castle.
As soon as Happily Ever After finishes (or if you can bear it, just
before it finishes) go straight to the exit, and head towards the bus stop for Disney's Animal Kingdom Lodge. If you can board the first bus, you should reach your dining reservation at
Jiko - The Cooking Place in good time.
If you are driving to Magic Kingdom Park, and therefore need to head back to the Transportation and Ticket Center using the ferryboat or the monorail (for the parking lot for all guests of Magic Kingdom Park) I don't think you'll have enough time, and I would highly recommend you change your dining reservation to at least 30 minutes later.
I hope this works for you! I totally understand that you don't want to miss either of these lovely events! I love the fireworks, and it would be sad to miss the ending.
Please come back and visit us if you have any further questions. We are always happy to help you plan your magical vacation to Walt Disney World Resort!
Sue