please tell me, how much time will be required to prepare for "collection" topic? how to best prepare "collection" topic in less time. which points / exam objectives should be kept in mind while studying this also which points should be given more importance.
Depends on the exam you take. For the 1.4 exam, you will need to know what type of collection to use in a certain situation and what each of the collection objects do (features, are the methods synchronized?, etc.). I studied the chapter on collections for about a week although I had significant work experience to back me up. I would say if you're coming into collections blind, take triple that time, so 3 weeks.
I highly recommend the study guide written by Kathy Sierra and Bert Bates. ISBN 0-07-222684-6