When Does the LTP Two-Year Payback Start?

For Boeing’s LTP payback policy, does the two-year payback period start after each class is completed, on a rolling basis? Or does it begin after the entire degree is awarded?

For example, if I take two classes in one semester and leave two years later while still working on the degree and did not complete, would I owe for those classes? Or only for courses completed within the last two years?

Thanks for the help!