Yes, you can test your SAML connection before SSO enforcement is put in place.
When we first enable SSO for your organisation's users, it will not be enforced by default and no user login sessions will be ended. You'll still be able to use other login methods to authenticate users.
Once you've confirmed that SSO is working for your user base, the Support team can enable SSO enforcement. If you haven't already raised a request, you can contact us here if you'd like SSO to be enforced.