There are two methods of backing up your timers on iOS.

First is iCloud. If you have iCloud Drive and Seconds enabled within the iCloud settings on your device then each time you make a change to your timers a backup is created and saved to iCloud. You can restore a backup by going to Settings > iCloud Backups and selecting the backup you wish to restore.

The second option is to backup your timers by exporting them from the device.

Android users only have the option to export their timers from their device.