Try going here TurboTax Easy Extension and click File a Free Extension and use your TurboTax information to log in and go through steps from there, if you are receiving that mid-March message when clicking File an extension on the welcome page when logged into your account.
Or when you log into your TurboTax account, click Tax Home (do not click Take me to my return here) to the left and then look in the bottom left corner above Sign Out and click File an Extension there instead.
