Use the drop down menu to go to Preferences > Backup > Backup folders: you can save up to three different scheduled backup locations and set the frequency anywhere from 15 minutes to weekly.
However from the Help link it says "Note: backups are only made when pressing the 'Save' button.", which would indicate that it's not actually automatic - it would seem that the point of scheduled backups would be that they would be automated...
"Backup folders (scheduled backup)
To ensure your work is always safe, it's vital to also back up your project to off-site locations, or at least on a different computer or hard disk. (Backing up to a Dropbox folder is specifically recommended as a free and straightforward off-site backup.) To help you do this, Construct 2 can save your project to different folders at regular intervals. You can choose up to three backup folders and the time interval that backups should be made. Files are saved as single-file (.capx) projects with some random text appended to prevent two identically named files in different folders overwriting each other's backups (e.g. myfile-abc123.capx and myfile-def456.capx). Note: backups are only made when pressing the 'Save' button. Simply opening a project that somebody has sent you will not make a backup for it unless you modify it and click 'Save'."
Can anyone clarify this?