The USCIS Field office in Orlando is normally one of the quicker offices in the south. The I-485 process is normally completed within 4 months. This can take longer if any red flags are raised within the application - prior applications, prior overstays, etc. Remeber once you file you can track your application on the USCIS website witht he receipt number you will get back from USCIS.
Congratulations and good luck.
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.
The fact that the visa itself has not expired is not determinative. Your fiancé's authorizes stay is controlled the validity dates of her I-94 card. I suggest you schedule a consolation with an experienced immigration attorney who can review your case and advise you and your fiancé what to expect and the costs associated with representation and filing with USCIS.
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While written by an attorney who is a Florida Bar Certified Specialist in Immigration and Nationality Law, the statements herein should not be construed as legal advice. No attorney/client relationship has been created without a formal consultation with the attorney and the attorney has agreed to accept your case.