Interests are paid every 30 days (counting from when you started the savings).
If, inside those 30 days, you take out something from the savings, you will break the cycle and lose the whole accumulated interest till that point.

In short, when you start the cycle, you can add more HBD in, but don't take anything out till the 30th day.
When this 30-day period passes, you can claim your interests. By claiming it, they (the interests) would be automatically added to the amount in your savings, by which a new 30-day period will start if you decide not to take anything out.
If you decide to take something out, the new cycle will start with the new smaller amount.

If you are going to use PeakD interface, you'll see in your wallet how many days ago your last payment (that triggered the start of the cycle) was, and as well you'll see how many days are left when you will be able to claim your interests.

We hope the above explanations will help you, at least a bit, to clarify and understand how HBD savings work!?!
!ALIVE