How to sit 18 productive hours for studies?

All covet all loss... Be moderate in anything.. No one can concentrate on one subject for more than 45 mins.. There is something called law of diminishing marginal utility.. Dont feel too much pressurised..of course some tension is necessary..But anything beyond limit would play spoilsport.. After all, at 60, what would count is how peacefully we lived and not how many marks we scored in ca exams..

study for 2 hours,,,, take 15 min break to increase eficiency , then REPEAT IT, sleep for 6 hrs...... 30 min each for 4 time  meal, so 6 + 2... 8 hrs will be gone in sleep and eating. remaing 16 hrs .. study by taking 15 min meaningful breaks..... this is the best possible method... which level you are talking about??? ca final???......................and one more thing.... one requires 18 hrs study like CHATUR in 3 idiots, only if you are doing ROTE learning... in ca final conceptual understanding matters.... however .... your first revision would definitely take more than 15 hrs per subject because of VAST syllabus...... 18 hrs study is a myth for intelligent students and a fact for rote learners...