This might be related to why you see the pop-up login box, in this post there's a reply saying:
one big requirement that is kinda nowhere documented
to use SSO your server needs to have HTTPS enabled (and it should be used exclusively) for NTLM auth to work (otherwise the site is "not trusted", because only https sites can be trusted).
I don't know that this is correct, but I've always used HTTPS for sites using SSO and I notice your site isn't using this from your screenshot.
However, if it's taking five minutes to authenticate when credentials are supplied manually that suggests there's a second problem. Can I suggest timing exactly how long it takes? Because if it is five minutes exactly (or almost exactly) that sounds like a timeout as if there's something misconfigured to do with DNS or AD. Is your IIS server separated from your AD domain controllers (e.g. in a DMZ) or is it able to talk to these on a "local" subnet?