How long back can I go?
Every change from the last 24 hours is saved. After that it will be combined to 1 file per day, and saved for 10 days.
It is also possible to add tags to individual versions. When a tag is added to the version, it will no longer be deleted based on the default time scale and will persist.
What is being saved?
It's important to remember that these autosaved versions are only saving information from the Configuration tab. Although if you change things related to configurations, from the Home tab, it may also be saved, and therefore revertible from the History View.
Example: Adding a Panel on the Home tab will not be part of an autosave, but choosing a configuration for it will.