What is considered as receipt date of I-485?

I am aware that I can change jobs 6 months after filing for my I-485(which is the receipt date on my I-485) without refiling for labor certification. My lawyer had filed for my I-485 on Nov 1st, 2020. So I believe I will be good to submit my resignation on 1st May 2020. However, I haven’t as of yet received my receipt. I was wondering as to what is considered as receipt date? Am I safe 6 months after date of filing which is Nov 1st, 2020 or 6 months since I receive my receipt(which will be future date)?