The Fireworks Spectacular begins just after sunset ... wait. Since when does the sun set at 6 a.m.? Well, according to the in-game calendar, fireworks will be going off hourly in all capital cities and Booty Bay, starting at 6 a.m. realm time or sunset. Apparently.
So go forth and get all of your Midsummer achievements done. Or just soak up the massive XP, gold and buffs. After all, the next official in-game holiday isn't until September.
Shameless plug: <It came from the Blog> will continue to run events at least once a month, whether there is an official holiday or not.