From the TBC Help:
Set a Reminder to Save Your Project
Use project management options to set a timed reminder that prompts you to save your project. When enabled, the Save Reminder dialog appears at an interval you specify.
Caution: Any time that you save your project, the 'stack' of actions that you can undo is cleared; you cannot undo past the last time you saved.
To access the command:
Select Options > General > Project Management.
I added "autosave" to the topic as a keyword to make it easier to find.
David