Turbo Tax - submitting electronically for review

[Mark5000]

When I used TT last year, I submitted my tax return and then tt reviewed it before submitting to the IRS. How does the deadline work? If I submit for the first time on April 15th am I "on time". What if tt requires me to make changes and I have to re-submit after the 15th - would I then be late?

Thanks,

Mark