H1 to H4 Conversion timelines

I am currenly working on H1B Visa and it expires on 09/30/14. This will be my first renewal and unfortunately my employer would not extend my H1B visa. I am planning to change my status to H4.

What will be the maximum timeline to start the process for H4 in this case?

Can I still be on H1 while I start the H4 process or I should resign my current company and then start H4 process, so that I can stay in US after 09/30/14 on H4?

Thanks

You have until 09/30/2014 to file the H-4 change of status. It takes about 3 months to obtain the approval. If you file before 09/30/2014, you could continue working while you wait for the change of status to be approved (but you have to stop working on 9/30 if it is still pending at that time). Or, you can stop working as soon as it is filed.