The time line for completing the survey of BTI-SGNR doubling has not yet been finalized. You can check it on NRs website. Also one most not anticipate the doubling work to be started before 5 years at least. Reason:
There are 4 doubling surveys from BTI station has been announced. Among them BTI-FZR will be the first one to complete as it is the main line and SGNR-BTI section is a branch line so there will be competition with the other 2 lines BTI-RPJ and BTI-SOG lines.