The IRS has not yet announced a date when they will start accepting 2019 tax returns. TurboTax will let you submit your tax return starting in the next day or two, but your tax return will not really be filed. TurboTax will just hold it until the IRS begins accepting returns. Nothing will be done with it before then. If you submit it early, be aware that you can't cancel it or get it back to make changes or corrections if you find that you made an error or left something out.
Also keep in mind that you cannot file your tax return until you have all your W-2s, 1099s, and other tax documents.
UPDATE JANUARY 12, 2020
IRS Free File and TurboTax Free Edition are available now. The IRS has announced that they will start accepting and processing 2019 tax returns on January 27, 2020.