Hire a local family lawyer to assist you.
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Unless your Decree says that if you give her advance notice you can change the time of exchange, she has not violated the Decree. You do not have a basis for contempt. It is only contempt if you show up at the place, date and times designated in the Decree and she does not release the child to you. A lot of people want to shoot the messenger when they hear this. I am not saying she was polite or kind or mature. I am saying that it is not contempt. She has established a bad precedent. I'm sure she will want some consideration from her at some point, and you are welcome to return the favor OR take the high road.
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Hire an attorney. If she did not agree to the time change, there was probably not a denial. But get a lawyer to read your order and talk through it.
This answer DOES NOT establish an attorney-client relationship. This answer is based on the limited information provided and is not intended to be conclusive advice. There are likely other factors that might influence or change the advice after a more lengthy consultation.
Do not hire an attorney. Instead be at the right place at the right time. This isn't rocket science.
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