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 on Windows:

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.

Mac does not have a default system scheduler, so the time needs to be changed either using a 3rd party app that has this functionality, or you can change it in the file ~/Library/LaunchAgents/com.emclient.mail.backup.plist

If you want to change the backup time to the current time, you can do that from inside eM Client:

• In eM Client > Preferences > General > Backup uncheck Enable periodic backup
• Click 'Apply'
• Enable periodic backup again
• Hold the Alt (or Option) key and click 'Save & Close' or 'Apply' - this should change the backup time to the exact time you changed the setting.
• Restart launch agent - open terminal and run these two commands: 
• launchctl unload ~/Library/LaunchAgents/com.emclient.mail.backup.plist
• launchctl load ~/Library/LaunchAgents/com.emclient.mail.backup.plist

The default time for the backup on macOS is 10:00 AM.