I want to play on a different ranked schedule and heard we're supposed to be able to select one each week, however I've never been given the option to?
The ability to select a schedule was only a thing for the first week of ranked. After that they changed it to have a single wider span of hours per day instead of 2 narrower spans. Everyone has the same schedule now and there's no choice involved
Not without some kind of outside meddling. From what I understand ranks are affected by which region you are from. You can imagine that people from EU who don't play ranked during hours people play them in the US, so they don't get matched against or with each other. Wouldn't make sense if someone was beating up games in one pool and get ranked in a global pool because afaik we don't have a global ranked pool because we can't have one due to time zone differences.
A high rank in US might not be as high in EU or vice versa.