This question is really difficult to answer. It depends on your circumstances and your will to study. Let’s say that you have no other work than to study. How many hours of study should you do?
If you are preparing full time for IES than please take it seriously especially in last month. Try to make a schedule which should coincide with the timing of exam. This will help you in maximising your brain effort at that time. Don’t make out of sync schedule. For example , students study late at night and don’t focus on their metabolism. Please sleep at night and study in daytime because your exam will be when sun is out. So 6 hours is minimum study that you should do. Make a sitting of 3 hours each because your subjective exam will be of 3 hour duration at strech. This is the world of cut throat competition if you are a general category student. You can’t leave anything to chance. I would say that study as much as possible even if you are an intelligent student. If you are able to cross the threshold of 10 hours a day for last 3 months, then success is definitely yours.
Don’t try to copy some another student’s strategy, make your own plan. No of hours don’t matter as much as understanding but as a rule you can say that-“the more you study, the better it is.”
Those who can do it , I would say try to cross 12 hour a day barrier for at least 15 days before the exam. It will prepare you mentally to sit for long hours on examination day. You need consistency and strength to go through continuous 3 day examination. It comes only if you practice.
I can suggest a time table here if want to follow it. Consider that you are preparing full time. This time table is to be followed in normal days ,in exam times you can increase the timings.
Morning session -9am to 12 pm
Afternoon session – 2pm to 5pm
Evening session – 7pm to 9pm
Night session- 10pm to 12midnight
Total=10 hours for at least 9 months and success is yours.
Best of luck to all.