#1. HOW MUCH TIME IS NEEDED FOR PREPARATION ?

Now time is money here .. it all depends on whether you are dropping or just preparing during internship. Keeping that point apart, you should make a time table of yours in which you should mark a deadline for each subject.
Make sure the amount of time you allotted for successive revisions are less than the earlier one. So if you plan your study this way then you will get a rough idea about the level of preparation you will be doing at the end of preparation.

#2. IS IT NECESSARY TO DO THEORY?

Now there are many people who give a different formula for entrance prep, but you all should know one thing that nobody guaranties you the success.. but yes.. they do give a hope. Somebody has said the truth. “ To know the path ahead, ask those who are coming back” . This just means that if somebody has got success then you surely have a hope in that path. But each you all should remember one thing, every individual is different.
Hence the amount of effort put by each individual is different and luck too. But one thing you all should remember is, YOU REALLY CAN’T SAIL IN TWO BOATS AT A TIME. The best advice to you all : trust one , and follow ii. Don’t complicate things by listening to too many people.
Ask one person who got a true success and follow it.What matters is the amount of trust you put in his words. That’s what is important to keep yourself motivated.
It also depends on your time and how you have read in your BDS days. I never had time to read theory in my internship but I had worked hard during in my UG, so I was not much scared about the standard books. But those who have taken a break of another year , I advise them to read the theory to because they have lot lot time for preparation.