Hi

9th standard will be a little early to start preparing for neet as child becomes stressed later on.

10th standard or preferably 11th standard is the best class when one should start preparing for this exam .

This exam requires lot of practice and understanding so 11,12 are the classes one when can strategise their concepts more fundamentally.

Furthermore you can find out more about study plan, timetable, books, subjects from link attached

https://www.google.com/url?sa=t&source=web&rct=j&url=https://medicine.careers360.com/articles/neet-study-plan/amp&ved=2ahUKEwiQvMXU15DxAhXr3zgGHfjCAugQFjAAegQIAxAC&usg=AOvVaw1MVYb05Mptw2j6PkCMZfPP&ampcf=1