Each time you make change and save your timers these changes will be backed up on iCloud.
iCloud Backups should be enabled by default. If no backups are listed on this screen you will need to check your iCloud account. You can do this by navigating to Settings app > Apple ID > iCloud and then ensuring that both iCloud Drive and Seconds are enabled.
To restore a backup simply tap one of the backups from the list. Restoring a backup will overwrite your current timers.
There will be a backup of the overwritten timers that you can restore in case you realise you have made a mistake.
Each time you restore timers any further changes will be backed up to a new file. This way there is no way you can lose your data.
Deleting a Backup
You can delete backups by swiping to the left across the row and tapping the Delete button. Or, tapping the Edit button, tapping the delete icon and then confirming with the Delete button.
Once a backup has been deleted there is no way to recover it.
Deleting All Backups
It's possible to delete all your iCloud data at once within the Settings app. Navigate to Settings app > Apple ID > iCloud > Manage Storage > Seconds > Delete Documents & Data.
You can restore backups from other devices that are using the same iCloud account. This means you can restore backups from old devices, or from an iPad onto your iPhone.