Day One data can be included in iCloud device backups on all iOS devices. Follow these steps:
- Go to Settings > Account (The first item in Settings) > iCloud > Storage > Manage Storage on your iOS device.
- Tap on your current device under Backups.
- Enable Day One under Choose Data to Back Up.
- Go to Settings > iCloud > Backup and tap Back Up Now.
This will include Day One data to iCloud Device backups. If you ever need to replace or restore your iOS device, you can restore from the latest iCloud Device backup and recover your Day One data. Data will be restored from the most recent device backup stored in iCloud.
For more information about how iCloud Backups work, see: https://support.apple.com/kb/PH12519