There is confusion here.
If you want to file today (May 1), just file. The IRS will apply your extension automatically based on your address. Don't worry if turbotax thinks you are late.
If you want to request a further extension to October 15, you must mail a copy of form 4868 requesting an extension, and it must be postmarked today. You may want to use a mail service that includes proof of mailing and proof of delivery. (Turbotax can't process an electronic request for extension after April 15, but the IRS will give it to you based on your address if you apply by mail.)
