Hai, When is best time to write Maths2, Phy and Chem tests for CBSE Board Students (India Board).
Chemistry:
Most of the SAT Chemistry topics are similar to those studied during the first half of eleventh grade (NCERT Chemistry Book For Class XI Part 1). So I would recommend taking Chemistry after the first half of class 11 which would be from October to January of your class 11.
Physics:
Most of the portion of SAT Physics is covered in class 11 but it has some class 12 topics like-
Electricity
Magnetism
Optics
Atoms, Nuclei
Modern Physics
Atoms and Nuclei topics for SAT Physics are similar to those learned in class 11 Chemistry. These topics along with Modern Physics are pretty small so they can be studied easily. Optics consists of Geometric and Wave Optics. Geometric Optics is pretty much the same as you would have learned in Class 10. The Wave Optics portion for the SAT Subject Test is not very long and that too can be studied easily.
You may however, want to study Electricity and Magnetism in Class 12 before you write the SAT so I would recommend writing Physics after say, a month of beginning grade 12. You could also take it before starting class 12 if you don’t mind studying it prematurely.
Maths II:
You could write Maths II after 2-3 months of class 12. You may find it easier to write it halfway through class 12, but I wouldn’t recommend it then as you may be very involved in studying (for Boards etc.)