H1b extension applied after expiry date

My h1b approved for FY2019, my attorney got approval notice yesterday that is feb 22, 2019 and it approved till March 1, 2019 so I have only 4 working days to apply for extension, applied for LCA on feb 22 and waiting for approval
My question is, how many days it will take to get LCA approved ?
If my LCA takes more time, is it ok to apply for extension after the expiry of my h1b that March 1 ?

Usually, it takes up to 7 Working days. Considering your situation, your attorney can put in a request letter stating your situation and act as soon as they can to file the extension. It is a tricky situation and you need to discuss with your attorney on this and take decision. You can read more at What is LCA, Processing Times