Receipt number not yet received from USCIS


My file is reached by USCIS on last day of my I-94 expiry date for my B1 visa extenstion. Currently 15 calender days are completed eventhough not yet received the receipt number to know the status.

Please provide me the clarifications for below questions

Is there any problems to stay without having the receipt number and I-94 expired?

How long this will took to get file numer for premium processing?