Urgent - I-94 expiring(B2) pending I-140 and filing 1-485

[sailingfamily]

We have a receipt for I-140 filed on exceptional ability ( EB1) and are intending to file I-485 this week. While this is pending our I-94 issued on a B2 visa expires in two weeks time. If the 485 is receipted prior to expiry of I-94 is are we still in status? and if it is not - does the receipt date of postage matter /count- (which will be prior to expiry) or should we be apply for extension to stay - not sure what to then say re application pending for I-485?
Thanks