Your prior year tax returns will have a Postmark Report if you e-filed the tax returns. The Postmark Report will have the date/time the tax return was e-filed and the date it was accepted.
To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download/print return (PDF)