What is the probable date of starting of cbse class 12 board examination and the probable time table?

However, tentative dates for exam will be Feb last Week or March first week of 2018.
Result shall be announced in May most probably.
So you have 3 months of preparation left, and you should be focusing in giving ample of exams to gauge how much you score and where yhere is cope of improvement.
Keep revision of weak areas and mostly formulae.
All the best.