How many hours should i devote towards iit jee preparation in a day, if im in 11th std right now? Also, I havent joined any coaching classes, everything i do is through self study...should i join any classes?

u should join a coaching class. i prefer u join FIITJEE. There u can  get an idea about about the type of questions asked in iitjee and other engineering exams. Always try to remain update with ur studies. Spend atleast 10 hours a day in studying but quality matters a lot than quantity.

you can take iit books and prepare those books you may study daily atleast 6 hours and you listen consantrately what was tell you your teachers in collage and practice intermidiate books perfectly