If you are using the same App Store account you should download the same version you previously had. If that was the paid app, download that again for free. If it was the free app, download it again, tap on the upgrade notice and then tap Restore Purchases.
You may be able to restore your timers from an iCloud backup. Check Settings, iCloud Backups to see if there are any to restore from. If not, as timer are only otherwise stored on the device there will be no way to recover them if you no longer have the old iPad.