Levels don't matter that much in EV training, because EVs take affect at level 100 (Unless you're playing Gen 3 or 4). If you're training to level 100 anyway, it won't matter if you EV train along the way or when you get there.
The time the Pokemon evolves has no effect on EVs. You could stop your Raboot from evolving until level 99 and it's EVs wouldn't change. It's base stats would though.
If you're playing Sword/Shield though, the best way to EV train your Pokemon are seminars and vitamins. You can find more information here.