Help with changing from Orange France to Free network

Hi Everyone, Having used the service for a few months and found that it really is 2 euros per month sans engagement, I now want to move my partners mobile number from Orange to Free. I got the rio code from Orange because it’s important that my partner keeps the same number. I’ve given this number to free. I don’t know how long it’s going to take Free to take over the number so I don’t know what cancellation date to give Orange. Has anyone had any experience with doing this who could give me any pointers please?