Question: when is the best time to evolve an eevee?
Answer: The best time to evolve Eevee is just when you get it, in Celadon Department Store buy a Water/Thunder/Fire Stone and to evolve it right away. To get Umbreon or Espeon, a good way to evolve him earlier is to give him 10 Proteins and other things like this and it will be an Umbreon/Espeon level 26.