I just released FreelanceStation version 1.4. This new version includes integration with Apple Reminders and a Time Log.

The integration with Reminders requires enabling the feature in Preferences and setting a default reminder list:

Calendar Preferences

When you create a new invoice, a reminder will be automatically created with an alarm set to the due date. You can opt-out of the reminder by clicking the Toggle Reminder button right next to the Cancel button in the invoice editor.

The Time Log window shows all time entries you have recorded. It can be open by going to Window > Time Log or by pressing ⌘3:

Time Log window

In this window you can edit the time entries and export them to CSV.

You can download a free 30 days trial here or purchase a license in the Mac App Store.