We did the Roof tour in the afternoon and because of the limited time to tour the interior of the Cathedral, we were able to go back the next day. In order to do that, we let our Rooftop tour guide know and he had a sign-up sheet for our return visit. (When going to the afternoon visit, we met at a completely different entrance from the regular Cathedral entrance). As far as visiting on the same day, prior to the scheduled Rooftop tour, I think it's a matter of entering in the normal entrance. Having said that, I wouldn't want to mislead you so you should make further inquiries as to same day visits. Hope that helps.