How soon can I safely buy decent facevalue seats

Hi guys, I've been dying to get down to Miami for a ballgame specifically when the Cubs come to town, especially since you guys built your new ballpark. How soon would this Cubs fan need to buy in advance for four good seats for a that Saturday afternoon game June 24th? I'm in Tampa now, so getting to the ballpark day of shouldn't be too much of an issue am I right in thinking that?

Thanks in advance guys.