Hi Nergal. Actually, whatever time is best for you is what will work for you. I do most of my work in the morning because it is more conveinient, however I get in some energy work (and sometimes meditation practice) while I wait in the car line for my son at school. So there's no wrong time- whatever works for you, however I would also practice mind clearing at nighttime, since you're already in the dark silence...
As for affirmations, I think you should translate it to your primary language. (The one you use the most.) Even though my primary language is spanish, I don't speak it much, so I do them in english, for it's the language I think in now.
Good luck in your efforts.