The number of accounts only represent how many have received the interest payments in the given month. In this case it was November. Total number of accounts that hold HBD at a given time might be different. However, I would guess it would be close, looking at number of accounts from previous month.

To receive the interest payment, the account owner must claim it or trigger a payment by transferring or receiving HBD. If no actions are done, account will continue accumulating interest and will receive the total payment when claim or trigger action is done. In other words, there might be some accounts that hold HBD and do nothing, they are not counted in the total number of accounts in this list.

There can be only one payment within 30 days. Blockchain would know how much each account has earned, based on how much HBD was in Saving at various times. I don't worry too much about detailed math. I am sure situations as you describe can be calculated. In simple terms, I would expect interest payments after 30 days. PeakD wallet gives an option to claim HBD interest payments.

Claiming interests regularly can help with compounding the interest.