Several new options have been made available in Friendly Competitions on the Pokémon Global Link (PGL) for Pokémon Ultra Sun and Ultra Moon. Until now, you could select the battle time to be 10 minutes or 30 minutes when creating a competition. However, as of today, you can now set up Friendly Competitions that have five minutes or 15 minutes as the time limit.
Source: Serebii
Pokémon Blog 