H4 question, thanks!

My situation is I am J2 , working with EAD which will expired on July 24th,during July 25th to sept 30, I have to change my J-2 to H4 because my hu*****and changed his status. Now I am applying for H1b which will be valid in Oct 1st( which is still in pending). The question is for filling the I-539 form,the question in the part 3 No 1: I request my requested status to be extended until MM/DD/YYYY, for my stituation should it be 09/30/2005 or the date same as my hu*****and's H1B? Someone told me to fill the date as my hu*****and's H1B expiration date.
My concern is my h1b is possibly approved before my H4 application, if so, then after Oct 1st, then I have 2 visa status, H1b and H4. however H4 is approved after H1B, is that means my status will change to H4 automatically? or I can choose H1b as my visa status?

A little complicated question, huh? Thank you for your help!