I tried that and it had no affect on login time. After some more searching I found this article: LDAP logins are slow or timing out which said disabling LDAP referrals can considerably improve LDAP login times.
After disabling this in Ignition (below image), the problem seems to be resolved.
I’m still curious as to why referrals slow down the login process but it’s resolved for now.
Thanks again for your assistance.