Hello Catherine!
Fantasmic! is my favorite show at Walt Disney World and is a can't miss attraction for my family. Since it is one of Disney World's most popular shows, it can become quite crowded so luckily Disney will add a second show to allow more guests to experience this masterpiece of pyrotechnics and story telling. Even when Hollywood Studios is not hosting Extra Magic Hours in the evening time, the second show is most likely not as crowded as the first. Since the
Fantasmic! Dining Package is only valid for the first show and most parents with children opt for the first showing, you can bet the second show will likely be less crowded than the first.
On nights when Hollywood Studios is hosting Evening Extra Magic Hours and there is a showing of Fantasmic! during those hours, guests staying off property are still welcome to view the show. Since most guests will line up well before the show starts, they will already be in line before the parks official close to the non Disney Resort guests. Either way, I usually recommend the second showing of Fantasmic!, it is generally less busy. I hope this helps and please let us know if we can answer any more of your questions!
Enjoy your "Disney Time!"
Mandy