1. There is no fixed time limit for replying the notice unless mentioned in the said notice though unreasonable delay should be avoided.
2. Properties are not registered, the title deeds conveying the properties in other's names are registered. So, your Aunt only can register a sale or gift or cancellation deed for transferring her title of the said property. The said property can not be re-registered by any body other than your Aunt.
3. The property belongs to her as per the title deed shown in the records. It has no connection with her filing divorce suit against her husband.
4. However, her husband can file a declaratory suit praying for a declaration that the property actually was purchased by him in his wife's name and he had paid the full consideration for which the property belongs to him. He can also pray that the Registrar should be directed to cancel the said sale deed in favour of his wife. This case will take around 5/6 years to be disposed of.
5. If her husband files such declaratory suit, your Aunty shall have to contest the said suit claiming that the consideration for buying the property was arranged from the fund she had brought from her father during her marriage or was earned by her. Her husband will not be able to do anything thereafter.