the correct strt.. to crack jee is regular stdies with full concentration.. it not about how much time u study,the quality study is important.....regular test in improtant t judge ur way... correspondence course can be a good option to manage ur preparaion.... brlliant tutorials correspandence course are good..
affectance of boards examination by jee i think by far a person individual choice or capacity .If u are going for jee then their is no point u shld worry for board marks .I studied for jee and didnt prepared fdor board anyways....and studied only after 20 feb for boards and still end up getting 94% marks(cbse) and clearing jee.........but their were friends in my class who said we dont study for boards and they didnt studied for jee either .They used jee as method to escape and told parents and teacher that they are studying for jee so they dont get marks in school.....u might not get marks in school that is normal but u shld have belief in urself that ur really studying for jee and not taking an escape route......and at this stage u shld not worry abt boards maks.period.
PS:- i got not so good rank of 6280 at jee but that is something not concerned with ur question and that has not to do by large anything related to boards exam.
adversities cause some men to break other to break records............i m of the other type....... :-)