You can backup the database at any time by clicking Tools and settings -> Backup now.
If you want ManicTime to make a backup automatically, you can set up Scheduled backup in "Tools and settings"-> Settings -> "Scheduled backup"
Restoring the database form a backup
In ManicTime, go to Tools -> Backup and restore -> Restore and point to ManicTimeCore.db.
What to backup?
ManicTime uses two databases, ManicTimeCore and ManicTimeReports. ManicTimeCore contains all the data you need to restore and it can be very small. ManicTimeCore is about 1/10th of the size of ManicTimeReports. ManicTimeCore will be included in every backup.
ManicTimeReports - restore will be faster. Also, if you want to import timelines form one machine to another machine via Import ManicTime timelines plugin, you need ManicTimeReports.
Screenshots - if you also want to backup screenshots.
Generated screenshot thumbnails are not included in the backup. The original screenshots are included when you choose to back up screenshots.
When restoring a backup that includes screenshots, you can choose the folder where ManicTime restores them. Check that the destination has enough free space before restoring a large archive.