Pokemon Survival Eevee Location

Hello!
Jolteon is my absolute favorite Pokémon, and I've been aching to get one on Pokémon Survival. But, even before I have to find a bunch of rare Thunderstone shards, I need to find a supposedly ultra-rare Eevee. I've heard that Eevee has a small chance to spawn (I've heard everything from 1% to 0.0001%) during the day in birch forest biomes. Is this correct? If not, what biome does Eevee spawn in, and what's the exact percentage? Also, does the time of day really matter?

Thank you for your help!

 

Thank you so much!