The April 15, 2024 date is only if you have taxes owed. If you do not have taxes owed or you are receiving a tax refund there are no penalties for filing after the due date.
But if you do have taxes owed, your tax return was filed on time and the IRS knows when it was filed so even if it is still pending on April 16, 2024 this will not be an issue.
Also, since this is the time of season when the IRS gets flooded with e-filed returns it may take over 48 hours before the return is Accepted by the IRS.