how much time should be suitable for the preparation .I have worked in sql,pl/sql ,have a exposore of oracle architecture , backup & recovery, done sql tuning ,but not any other type of tuning.
Thanks in advance
If you are doing nothing else, and you have prior exposure as you say, one week thorough preparation per exam should be sufficient to pass.
I may add that it depends upon individual and circumstances. If you are working or have family committments, you can add time accordingly.