Knucklesugandan

I know Cimnabar Island is accessible after 4th gym (and obviously after getting surf), but I'm not sure about Cinnabar Mansion. Tried help chat, but they say Cinnabar Island is not accessible after 4th gym, which I know that it is, which males them not thrustworthy. The reason is because I want to do a PRO speedrun in a new account. xD