90 days out but I would also speak to your SM or co-ordinator to let them know what you're doing and to ask for a number where you can speak to the Restaurant Manager direct as I am under the impression that it's only the personalised menus you get through Disney Dining when calling for V&A's.
Definitely see if you can speak to the restuarant Manager direct although I still think you have to wait until the 90 day mark to book.