Files extracted from an archive have particular permissions that prevent SyncTime from accessing them before the process has completed. Only when the process has completed SyncTime is able to access the extracted files without errors. There are some workarounds:

SyncTime itself does not use encryption, but you can encrypt the destination volume and protect it with a password. When connecting a password-protected volume, you’ll be asked by macOS to enter the password; you can also store the password in the keychain so that you don’t have to enter it every time when connecting it…

At the core, both apps create copies of your data. Time Machine is designed to create incremental backups of your Mac. SyncTime can do that too (although it’s not allowed to access some system files), but it can also synchronize files and allows you to customize various settings depending on your needs. Time Machine is…