Generally, the DA has up to 1 year to file a misdemeanor DUI case against you. (There is an argument that can be made that a lengthy delay less than 1 year that prejudices your ability to fight the case entitles the defendant to a dismissal.) In other words, you still have to fight this case. I would get a good local DUI defense attorney to represent you in this matter. If you get a private attorney to appear, you do not have to attend court.
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Yes, they can file up to 1 yr later (after arrest) on a misdemeanor. Longer on felonies.
As for what to do to prepare for court, lawyer up. That will be your best bet. We can't tell you what research to do, etc., because we know nothing of the case.
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I agree with my colleagues that the DA's office has one year from the date of the incident to file on a misdemeanor DUI charge. Depending on whether the chemical test used was a blood draw, it can take time depending on the lab being used and what they are looking for other than alcohol. If the arrest was for alcohol only, I hope you contacted an experienced DUI attorney relating to any DMV administrative action to suspend your privilege to drive assuming your physical driver's license was taken and you were issued a pink temporary license. The best way to prepare is to consult an experienced DUI attorney in your area. If you cannot afford one, show up to court on time and if you qualify for a public defender, ask for one. Good Luck!