The Online web versions open in early December. You can set up more than 1 account to do practice returns or just use the same account. But be sure not to file any of them except for the real return when you are done.
If you buy the CD/Download Desktop program you can do unlimited returns so you can test different amounts. The desktop program is available now here,
https://turbotax.intuit.com/personal-taxes/cd-download/
The CD/Download program has many advantages over the Online version. But you need a full Windows or Mac computer to install it.
