Apple Upgrade Program/Loan Cancellation

Does anyone know when the old loan is cancelled out for the apple upgrade program? I’ve read that it’s when your new phone ships but that seems unfair.

For example, my existing loan charges me on the 12th of every month. However, I just ordered my new phone and it says that it will not deliver until at least the 19th of next month. If that is the case, am I going to be charged on both the 12th and the 18th (presumably when it ships) simply because of the timing of it? That seems unfair since it’s only a few days difference.