From the Super Mario Wiki
Sunset Beach is an unlockable court in Mario Hoops 3-on-3. It is classified as part of the Mushroom Tourney and is essentially Koopa Beach during a sunset, the only differences being that a red shell replaces the green shell design and the pirate ships do not appear. To unlock Sunset Beach, an exhibition match must be played on Koopa Beach between the hours of four and six PM (according to the player's DS's internal clock).
The rules are the same as on Koopa Beach.