Question: what time do i have to evolve eevee into umbreon?
Answer: Umbreon and Espeon both evolve after walking with the Eevee as your buddy Pokémon for 10 kilometers. Once that's done, the buddy Eevee evolved during the night will yield Umbreon while the day will yield Espeon. Note that when you evolve Eevee, it still needs to be your buddy Pokémon for this trick to work.