Transferring shares from physical to demat

How much time it takes to transfer physical equity shares from two  joint holders to single holder ( removing name of the joint holder) ?? and from physical shares  to demat ?? If the physical shares are not converted to demat before 1-April-2019 deadline , what will happen to those physical shares ? Will it become void ? or it can still be converted to demat even after the deadline ? Please suggest.

Thanks & Regards