Many factors such as age, prosecutor discretion, what judge you have, whether witnesses are credible all matter and that makes it near impossible to say what the outcome will be.
You can miss defenses and say the wrong things if you are not represented by an advocate as your attorney.
You might find my Legal Guide helpful "Ethics: Yes I Need a Lawyer!"
http://www.attorneyqna.com/legal-guides/ugc/ethics-yes-i-need-a-lawyer
You might find my Legal Guide helpful "How to Choose A Lawyer For You."
http://www.attorneyqna.com/legal-guides/ugc/how-to-choose-a-lawyer-for-you
You might read my Legal Guide "Can An Attorney Really Help?"
You need a lawyer. Check with a lawyer in your locale to discuss more of the details.
Good luck to you.
God bless.
NOTE: This answer is made available by the out-of-state lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney that practices in the subject practice discipline and with whom you have an attorney client relationship along with all the privileges that relationship provides. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question.
How much time you are looking at, as a practical matter, depends on the local practice. The maximum penalty for a first-time DUI includes six months in jail, fines, court fees and an alcohol program.
As for what you will actually get will depend on a variety of factors, including the local standard first-time offer, your blood or breath alcohol concentration, your prior driving record and record of criminal convictions, etc. Your best bet would be to consult with a local criminal defense attorney.
You also state that you plan on pleading guilty. Before you decide to make a plea, you need to consult with a lawyer. Within ten (10) days of an arrest for DUI in California, you must also demand your DMV hearing by contacting the DMV. (The information is on the pink temporary license you should have received from the cops.)
The reason you need to consult with an attorney is that DUI is a complicated area of practice and an experienced DUI lawyer can spot defenses you may not be aware of. These defenses or defects in the prosecutor's case can be used as bargaining tools to get a better deal.
If you can't afford an attorney, ask to have the public defender appointed so that someone can evaluate your case before you accept any plea offers. Neither the judge nor the prosecutor are very likely to change the offer just because you wanted to have an attorney review the police report and talk to you.
No. Do nothing until you speak to a private attorney. Or, plead not guilty at your arraignment, ask for the appointment of a public defender and then get a continuance to discuss the matter.
WIth the caveat that I don't practice in your county, I can tell you what I know about how these cases are handled in Orange County. Assuming there is nothing out of the ordinary about your case (e.g., you have no prior criminal record and committed no other offense at the time of the DUI), the chance of you getting jail time in OC would be zero. In 15 years as a lawyer in this county, I've never seen it happen.
I agree with those who suggest that you should still consult with an experienced attorney to determine whether you have a defense that might justify fighting it, or getting it reduced to a lesser charge. A .09 BAL is relatively low.
Best of luck to you.
Brian Gurwitz