H1 transfer to H4, but husband need to do H1B extension

Hi friends,

I have a question. I wanna switch H1 to H4 on May. However, my husband’s company will file his extension on April. The lawyer told us if I wanna submit H4 form at the same time, my H4 will start on this October. Is that means I cant quit the job on May?

If I want to quit job on May, shall I need to submit another H4 transfer before he start his extension? Shall I need to resubmit again at the same time as his extension?