FWIW Blizzard is 8-digit TOTP, they just don't make it obvious/easy to use your own stuff.

Here's a command line tool I wrote that will generate a TOTP authenticator for you, with QR, base32 secret, etc:

https://github.com/jleclanche/python-bna

You can use it with andOTP, KeepassXC, 1Password etc.