I think as long as your plants healthy and growing vigorously, then there isn't a wrong time to do it. I think plants enjoy a lot of their attention in the morning and then they can spend the day relaxing and healing...but some people may totally disagree with me and think the opposite is true. I just know I do a lot of morning work.
The only thing i can say for certain, is some strains/breeders have it pegged down as when to NOT top your plants...for example Ethos mandarin cookies you never top within 10 days of flowering.
Good luck and happy snipping.