One of the many commendations you can complete as you paint the sky with Fireworks and Flares is the Night-Time Spectacular commendation.
To complete this commendation, you must set off a display of five or more fireworks at night. To do this, you will first need to get your hands on some Fireworks.
Night-Time Spectacular Commendation
To complete this commendation, you’ll first need to gather some Fireworks. You’ll need at least five to get the commendation done.
You can either purchase Fireworks from the Merchant Alliance at any Outpost or find them in Resource Barrels scattered throughout the Sea of Thieves.

Once you have your Fireworks, load them up into your ship’s cannons and wait for night.
Once it is dark outside, quickly fire off your five Fireworks simultaneously or back to back if you are on a Sloop.
If you shoot five Fireworks off quick enough at night, you will complete the commendation.
It is possible to unlock the commendation by yourself on a Sloop. Just be quick as you shoot your Fireworks. You can also do it with a crew on a Galleon if you like. The crucial part of the commendation is to shoot five Fireworks into the night sky as close together as possible.