Wanda,
Thanks for asking your question to planDisney!
I recently had lunch at
Space 220, and it was out of this world!
See what I did there?Unlike some other dining venues that feature an entertainment element, the experience at Space 220 is not on a schedule where you might feel inclined to stick around after you are done eating so you can see some other element of the show. So no, you won't stretch out desert to see that last princess. It is more of an atmosphere-based experience. As such, your dining time is not altered by the experience, and you should be able to be seated, eat, and depart all within an hour.
So let's guess that
Harmonious is held at 9 pm. I would not want to have a reservation any later than 7:30 pm, since you will want time to walk to the World Showcase for a viewing area. Personally, I would suggest you go for a time in the 6:00 pm to 7:00 pm window, or 3-4 hours before show time, to ensure you get a good experience at both the meal and the fireworks show.
WARNINGPlease remember, I just guessed at the Harmonious start time. You will want to check the Disney entertainment calendar closer to when you have to make that reservation.
BONUS TIPThe salmon was very good!
Write me back if you have any other questions!
Have a Magical Vacation!Doug