Form 7004 must be filed on or before the due date of the applicable tax return (March 16th this year).
For Form 1120-S:
A penalty may be assessed if the return is filed after the due date (including extensions) or the return doesn't show all the information required, unless each failure is due to reasonable cause. For returns on which no tax is due, the penalty is $205 for each month or part of a month (up to 12 months) the return is late or doesn't include the required information, multiplied by the total number of persons who were shareholders in the corporation during any part of the corporation's tax year for which the return is due. If tax is due, the penalty is the amount stated above plus 5% of the unpaid tax for each month or part of a month the return is late, up to a maximum of 25% of the unpaid tax. The minimum penalty for a return that is more than 60 days late is the smaller of the tax due or $435.
See https://www.irs.gov/instructions/i1120s#idm139641016307376
