You can execute a gift deed of the property by paying appropriate Stamp Duty and register it in favour of your mother.
List of necessary Documents :-
1. The present title deed
2. Share Certificate
3. Electricity Bill
4. Maintenance bill
5. Occupation certificate
The time frame depends on the lawyer to draft a gift deed. Once your papers are in order shouldn’t take much time. After document is registered, you will have to make application for transfer to the governing body (mostly CHS, in case of Flat) and submit application as per norms of such governing body. The body will take its own time to approve the transfer papers (generally in Managing Committee meeting) but actual transfer is approved during General Body Meetings ( in case of CHS) so the time taken for the transfer can vary according to the governing body rules and regulations pertaining to transfer.