New to v5.9.0, Tinderbox has an app-level preference "Autosave every 10 minutes" whereby all open TBXs - except read-only or unsaved ones - are saved every 10 minutes. The feature is enabled via an option on the General pane of Preferences. The save periodicity cannot be altered by the user.
From v5.9.1, Autosave doesn't trigger synching slaved to saves, such as with simplenote. Also, making a manual save will re-set the autosave clock.