When will be the entrance for b.ed admission in private ?

You can apply in month of April or may for the same. Classes start from July or August. Eligibility Criteria for doing B.Ed is Pass with 50% aggregate marks in Bachelors Degree or Masters Degree in Sciences or Social Sciences or Humanities or Commerce or equivalent

Or
Pass with 55% aggregate marks in B.Tech. Or B.E. With specialisation in Science and Mathematics or equivalent (Candidate must have studied the subject of the subject combination for at least three years at Bachelors Level or Masters Level)
5% relaxation for SC/ST/OBC and other categories as applicable. Some institutes conduct entrance exam where as in some institutes You can even apply directly for admission. A good universities are: Delhi University, Delhi, Lovely Professional University- Punjab, VIT University Tamilnadu, Jamia Millia Islamia University Delhi, NMIMS Mumbai, Anna University Tamil Nadu, University of Mumbai, University of Kolkata, Pune University, University of Hyderabad, Delhi University, AMU The Maharaj Sayaji Rao University, JNU Delhi. Savitribai Phulle University.

This time is peak time for admissions  , I mean from april to june in some good universities like Symbiosis University, Lovely Professional university, Lady shri Ram college for women- New Delhi, Kasturi ram college of higher education - new delhi, Guru Gobind Singh Indraprastha University- New Delhi

Good Luck

The application schedule varies college and university wise as there is no generic dates for all so please tell which one you are asking for.