hi,

see you must clear your doubts about course duration and timing with the coaching authority before enroll for any of the course. however if currently you are pursuing 10+2 course , your main focus should be your board exam and simultaneously you may prepare for others entrance test.

make a proper lecture notes, short notes and set up previous years solved paper, so that you may remember it after a gap of several months.

make a routine for study and daily work and follow it accordingly.

best of luck.