The backup options are accessible in Menu > Settings > General > Backup.
You can choose the folder where the backups will be saved and once you check the ‘Enable Backup’ option, you can also select how often you’d like the backup to occur and how many backups you want to keep (you can store up to five different backups at a time).

To change the time of the backup:

1.        Open up the Windows “Task Scheduler” tool
2.        Click on the Task Scheduler Library
3.        You will see eM Client Database Backup in the middle window amongst the other tasks – double-click it to open the properties
4.        Go to the ‘Triggers’ tab
5.        Now you can edit the time and day when the backup takes place.

Read more in the Documentation: Backup