Usually when people have problems doing a purchase or upgrade, the App Store is messed up. Try going to the Apple's Setup app and log out of the "Store". Then try the update again.
My only other thought is that you can do a BACKUP to Dropbox, delete Time Master and the go into the "App Store", "Purchased" (bottom tab), and do the "Not on this iPad/iPhone" (top tab) and download it again. Last go into the Backup & Restore, sign into your Dropbox account and do a Restore.