New H1 Filing in the last 2 days of valid H1 status

[Bageshree]

Hello,

My H1-B visa is expiring in next 2 weeks and I am transferring my job from company-A to B. The new company has started the process of H1 extension and transfer and the immigration law firm is planning to file the H1-b extension at USCIS in the last 3 days (before the H1 expiry date, September 30th). I inquired with the immigration firm and they said as long as USCIS get's my application before the expiration date I can port my H1-B. However I have few concerns,

1. How much time it takes to receive H1-B receipt after submitting the application? Is the H1 transfer application filed online/electronically or it is through regular mail post?

2. If they file my application on September 26th and I don't receive a H1 transfer receipt notice in the next 4 days (as it has 2 working days and a weekend) can I still qualify under the H1-B portability rule and can start working from October 1st assuming my receipt will come (because the lawyer has confirmed that he already sent the application)?

3. What if I have to just wait for the H1 receipt notice, in that case will I be out of status after my H1-B expiration date and how many days can I stay in this status (while I am waiting for H1 filing receipt)? I understand that I have to apply for some change of status but how much is the grave period once your H1 visa status expires?

Please let me know your suggestions at earliest.