... as long as you get the receipt notice before H-1B expiration, you'll get 240 day grace period starting from the expiration date, meaning during these 240 days you can still be on payroll and have legal status due to the fact that your renewal application is pending.
I'm hoping that it won't take more than 240 days to get approval. Worst case, premium processing can be used.
I'm in the same boat. Mine expires in end of Sep too. My lawyer has kept my application preparation work on hold for a month already since he's swamped with the July 485 filings :(