You asked how long I studied for the ICND2 exam. I have to be honest with you. This was my second attempt. I failed the first one with a score of 786. I took my second attempt only 14 days later while the info was still fresh in my mind. I told myself I wouldn't let up until I passed. Needless to say I feel like a huge weight has been lifted from my shoulders.
I studied for about 6 months prior to my first attempt. I used the following aids:
1. CCNA Exam Cram ISBN# 987-0-7897-3712-0 (I used this book for ICND1 & ICND2)
2. Online practice exam questions
3. This forum (I can't express how helpful this forum has been. The amount of experienced professionals that use this site is incredible. They respond quickly, and it's FREE! I strongly suggest you use it often to ask questions about content you don't understand)
One more thing. The exam is not easy. Don't get discouraged if you have a set back or two. That's why it feels so good when you pass.