I looked back through the press releases that I've seen and they don't say nightly, but the guessing is that they will be presented nightly because the Tomorrowland Skyline Lounge is being offered nightly starting April 13 (the dates on the website go through April 29). Typically, they only offer the Skyline Lounge on nights when fireworks are scheduled to be presented. So folks are using that as a "best guess" that the Pixar fireworks will be offered nightly.