The fees set up on your client's account as at the end of a given month (or as at the day when the client’s account is closed) will be the fees applicable for that month (or part thereof if the account is opened or closed within that month). These fees are charged to the client's account on approximately the 3rd business day of the following month (or upon account closure).
If there is insufficient cash balance to pay the fees, the fees will accrue and be charged in the next month's fee run, provided there is sufficient cash to cover both the current and previous month's fees.