Nobody has a view on your schedule and knows how much free time you have and you can put into this assignment. All depends on your experience, the level of perfection you want to pursue (it would take less time to score 320 out of 400 than time needed for a perfect score) and of course the time you are willing to sacrifice for this assignment.
I took about 5 months to finish the certification, but I had to combine it with a full-time job (so only evenings and weekends) and a bit of a social life. When I was developing I was sometimes watching the Champions League, so that's not the most productive combination
But there are people who finished their assignment in 1-2 weeks, others took 5-6 months.
This forum is an excellent resource and I think you can find every possible question you might have already posted and answered. And if you can't find the answer or you still have doubts, just start a new
thread and share your question/doubts.
And maybe Oracle extends the deadline another time (they already did that once, 1st deadline was August 1, 2011)
Good luck!