I said this to you in a thread, but the Twins are in the same time zone as Chicago and Milwaukee.
Cubs and Sox are already heated rivals. It would make things even worse if they were in the same division.
I'd make it 6 divisions, though ... and you can still have 12 teams in the playoffs ... 2 from each division.
6 division as I'd do it: NE - Boston, NYY, NYM, Phila, Balt; SE - WashDC, Atl, Mia, Rays, Reds; MW-east - Cleveland, T'ronto, Pitts, Detroit, ChiSox (although that makes the ChiSox the only team in the central time zone); MW-west - Milwaukee, Cubs, MN, StL, KC; SW - Houston, TX, CO, AZ, SD; West - LAA, LAD, SF, Oak, Sea