Yes, you can complete your return now and save it and sign out of the account prior to filing it.
Once you get to a spot where you would like to stop working on the return, click on My Account at the top of the screen and click on Save and Sign Out. When you are ready to continue your return, simply sign back in and choose to continue working on the return, then select to pick up where you left off.
The filing deadline to submit 2016 tax returns is Tuesday, April 18, 2017, rather than the traditional April 15 date.