Until the summer starts, the new nighttime show will most likely be a weekend thing.
I could see the show taking place on April 29th and 30th with the park being open until 8:00pm and then again on May 5th. On May 3rd the park is set to be open until 8:00 pm as well, but since it is not a weekend, I doubt the show will happen.
I also doubt that park hours will be extended because of this nighttime show. The parks start to clear out before the park normally closes during this slower time of year. I doubt there will be enough people left in the parks to see the show to justify paying all the team members for a few extra hours of work, not to mention the cost of keeping all the rides running.
Once the show starts this spring, hopefully they will announce the times it is taking place so you can plan what day to visit US.