Depending upon each pitcher and where they are in their progressions, they should be working on focused fastball bullpens. I use 7 weeks as the minimum time for prepping starters who intend to pitch 5+ innings. Use this time to first develop velocity and pitch counts. Be sure to focus the bullpens on clustering pitches to a single location to get a feel for each key spot. Never try to hit multiple spots in the same bullpen. The time for that will be when getting warm before a scrimmage or simulated game. Have catchers working on framing those borderline pitches. Be sure your starting catcher has at least some time with each pitcher. Ask focused questions and posters on this site can help better.