I took a 529 distribution on 29 Dec 16 for a tuition payment due on 3 Jan 17 and now I have an excess distr on my 1099-Q for 2016. Can I avoid paying excess tax in 2016?

If the distribution was made in 2016 and you paid the School in 2016 as well, you can adjust the amount of Tuition you actually paid in 2016. 

If this amount is not reflected in your 1098-T for 2016 you can make the adjustment by following the steps below. Please keep in mind, that if you adjust this amount for 2016, you will have to make a reverse adjustment to your 1098-T next tax season: 

1. Log into your TurboTax account and access your current return
2. From the Welcome Screen find and click on Federal Taxes then below find and click on Deductions and Credits and the select I'll choose what I work on 
3. Scrolls down to the Education Section and click on Visit All
4. Walk through and re-confirm the questions you may have already answered in this section until you get to the    Your Education Expenses Summary page 
5. On this page click Edit next to the student's name 
6. In the next screen find and click on Edit to the Tuition section. 
7. When you are in the area to edit your 1098-T under Box 2 you will see "What if this is not what 'the student' paid to the school?" click on this question. 
8. A box will come up, and you will be able to enter the amount you actually paid in 2016.