Emailing professor too early has any impact? I was just wondering when should we start contacting professor of grad school for admission. Does contacting professor too early cause any impact? like, professor gets irritated and never reply back again, blocks forever and things?
Any sensible professor would be happy to reply to a talented student with A+ results; and be more than happy to supervise one. 

The only issue with the time is, sometimes the good professors at a university can't take more students to supervise; because they are supervising 5-8 students for their final year projects. So, as soon as you can contact the professor, the better.