Can you clarify what happens after 30 days? If a user can't send coins to himself and start the 30 days over again, does that mean people won't get interest on coins they buy from other people?
Also, does the term APR decrease gradually, or every 16830 blocks?
When the value of an ordinary output (not locked) is calculated, the software only calculates interest for a maximum of 30 days - the user is free to move the balance any time and start earning interest again. Whoever owns the output gains the interest.
The bonus rate decreases gradually.