I believe you should give equal time to all the three subjects namely Physics, Chemistry and Mathematics. However, my personal experience suggests give a little more effort in Chemistry. In case everything goes well as per previous trends and Chemistry section in examination is Moderate, you will have immense benefits. Not only will you be able to score high in Chemistry but also finish the section in approx 40 mins confidently and give time to Physics and Chemistry Sections. This was my strategy for JEE Advanced, and I still believe JEE Advanced in more of a strategy than hardwork. You need a solid test taking strategy, a strategic timetable for regular preparation as well as strategy in selection of preparation materials.

HEY!

this is a trick question. can you ask what is essential to live among water, food, shelter? no right? like wise, all subjects in jee are important. maybe you can prioritize them.

from your strongest sub to weakest one.

in my case, ill do it like,

physics, math, chem and so on.

so keep the strongest in attention and weakest in most attention