CAT Preparation

If you are preparing for CAT exam then you don't need to prepare separately for IBSAT exam. The reason behind this is the topics which are asked in CAT exam are the same topics that are asked in IBSAT exam. So, both exams are almost same but the thing differs is difficulty level. CAT is tougher as compared to IBSAT. So, try to prepare for CAT exam because this can help you score good marks in IBSAT.
IBSAT exam includes Reading Comprehension, Verbal Ability (VA), Quantitative Aptitude (QA) and Data Interpretation (DA). Whereas, CAT exam includes Verbal Ability (VA), Reading Comprehension (RC), Data Interpretation (DI), Logical Reasoning (LR) and Quantitative Aptitude (QA).
So, both the exams are having similar content. Preparing for CAT exam can cover the IBSAT exam syllabus too and this can help a candidate in every aspect.

Here are my top few suggestions:
1) Learn tables till 20.
2) Learn the values of fractions like 1/1 = 1, 1/2 = 0.5, 1/3 = 0.33 and so on till 1/30. I have learnt the shortcut for memorizing this when I was preparing for CAT. You can find it somewhere on the internet. But learn it.
3) Learn the square of numbers till 30.
4) Learn cubes of numbers till 20.
5) Learn to visualize fractions as pies (pie-charts) and then apply calculations like addition/subtractions to it.
7) Learn more Pythagorean triplets like-3,4,5 - 5,12,13 - 8,15,17 and their multiples. You must be able to identify these triplets in problems. There will always be at least one problem on triplets.
8) Learn trigonometric ratios for popular right angles triangles like-45-90-45 and 30-60-90.
9) Finally, practice a lot.
Also, remember to keep your eyes open and be alert. Did you notice that I skipped point 6?
All the best.
P.S. I got 96-97 percentile in Maths Quant for 2 consecutive years.

A job with studies becomes a hectic task. But there are many people who do both at the same time.
Firstly, you need to plan and organize your activities. Like the time remaining after work hours, effective utilization of this time is needed.
Also, time spent in traveling should be utilized.
Start reading a newspaper like The Hindu, Editorial section to improve in verbal section.
Also, keep formula's /basic concepts ready on cards. So that you could read these cards during breakfast or idle time.
Also during lunch break or so see, News channels.
Things will become easy once you are sorted with the correct utilization of available time. CAT requires hard work, and there is no exception to this hard work. Eventually, these efforts will sail you through exams and make life better once you get a good college.
Also "Change of subject is rest to mind", so keep doing different subjects (Maths, LR, Verbal) inrotation.
Sometimes when tired, watch an English movie (will improve verbal).
This helps you keep work-life balance and prepare you for MBA.
All the best.

CAT is an exam where your basics need to be strong. They will ask you questions anyhow by combining two topics together or putting up a single topic example in a unique and different way.
The main topics that a student should prepare would be time distance, time speed, probability, ages, dice, ratio and proportions, etc., from Quants.
Verbal is considered to be the most difficult area in CAT exam as you need to have a strong hold on English language i.e you must be having a very good vocabulary, grammar should be perfect, etc.
For Reasoning, your focus should be on matrix puzzles, coding-decoding, sequential output, etc.
You need to be very strong in verbal and reasoning to crack CAT as these are the two main sections where you can score more than others if you practice well.
So, start with basics as those are the most important ones.

As per my experience I don't think that an year gap affects for CAT preparation adversely affects your chances of getting admission in any institute in IIMs or any other institute of India. The entire interview process is meant to gauge the students on their knowledge, skills and attitudes as well as their inclination of doing a MBA program.
If you are dropping out of your current job for one year there should be a justification as to what were the reason for opting out of your job. There are various examples of students who have scored a hundred percentile while working and thus the interviewers always discuss the reasons for dropping out. But, if you are able to justify it well and convince them about yourself. I personally don't think that it would negatively affect your chances into IIMs or any other institute of India.