The default time is day so you can simply get day evos by fulfilling their normal conditions, but there are also night evos in the game and they are actually triggered by moon stones.

Some stone evos actually bypass other requirements, but it's a bit inconsistent. ( I can get a level 3 Alolan Ratticate via moon stone but not an Aurorus despite both requiring a level up at night at a specific level . Probably bugged one way or the other.)