Hi there ZC! Always good to see you on the threads.
As a member of the parish RCIA team, and one who tries to determine whether our students are ready or unready to be admitted to the sacraments, I can tell you that you are misinformed about this. We would have no problem receiving a catechumen who was a creationist.
That God is the creator of all things, visible and invisible, is a doctrine of the Catholic Church based on Scripture. The exact way, and the exact time frame in which God the Father Almighty created heaven and earth, are not part of the doctrine of the Catholic Church.