Payment reminders go to each client's primary and billing contacts while an invoice is still owed, with a button to view and pay it. A client can be left out of reminders and statements on the Billing tab of its Edit window. Late fees above come every 30 days late, while reminders are on.
How the time logged on a billable ticket becomes hours on an invoice - in Unbilled Time, a ticket's Invoice window and Add Tickets. Each ticket's time is rounded once, as a whole. It is billed at the client's hourly rate, or the default rate in Defaults when the client has none.