You can correct your extension until the deadline date. However, if you happen to e-file your extension close to the deadline date, and if it gets rejected, you'll be given 5 calendar days (also for form 8868 and 4868) to correct it. This time period known as the Transmission Perfection Period is exclusively meant for correcting the errors in the extension.
For instance, if you file your extension on 3rd March, and if it gets rejected, you've time until 16th March (due date) to correct the errors and to re-transmit it. Instead, if you happen to file your extension on 13th March (close to the due date) and if it gets rejected, you'll be given 5 calendar days from 13th March to correct the errors and re-transmit. So, you get time until 18th March.