woocommerce single product page hook not working

Thanks WisdmLabs. I traced it finally after the discussion. The changes in product page are appearing now. Below is the mistake I have done.I am posting this as it might help others with similar problems.
In my plugin I am calling file B in file A using require_once. I have placed my function timeslot_display() and hook calling line in file B which did not give any results. When I copied the entire code of file B to file A, then I am able to see the changes in product page. Not sure why this happened but it worked.