***So would you please suggest how long ahead of time do we need to prepare and file the H1-B to H-4 transfer so that there is no gap between the H1-B and H-4.
***Is there any grace period between H1-B and H-4? What do we need to do with the above situation?
Do not worry. start to find a new job in your location now. Just /mail the I539 for H1B to H4 status change in the last day of H1B valid day, and make sure the USCIS can receive it in the next day, it should be fine.