The best place to see what you can do with payback days is explained in detail in the Scheduling Reference Handbook available on the Dalpa website. In good reader on my iPad, the answer is on page 104. Read all the questions and answers for what I said below.

Short answer, they become supplemental days and you bid them with next years vacation. There is a way to use them in the first 3 months of the year but you need to reference the above to see how to do that.

Denny