One possible cause of the long wait time is that you are not using a custom domain for Auth0.
The customizations to the universal login pages only take effect if the custom domain is enabled and used. This applies to all the pages/prompts (e.g. login page, mfa page, password reset page, etc).
Another possible cause is that you are redirecting users to the /login page directly, instead of the proper authorization request endpoint (e.g., /authorize if you are using OpenID Connect). The Auth0 documentation also states that you should always redirect users to the proper authorization request endpoint. If you redirect users to the /login page directly, they will get an error unless you have configured the default login route.