Efficiency on CNC milling

Hello,

I am writing on these forum hoping to get some help regarding organization in our mold shop. We are only a few people, but we have very good machines (Agie, Jung, Hauser, Mikron, Parpas) and I am frustrated how much time a day we lose especially on CNC milling.
We have two operators running three machines in two sifts and we run longer program (especially electrodes and hard milling of inserts) unattended over the night.
Unfortunately a lot of times happens that all of them are staying still while operator is preparing or editing programs with following corrections:
-preparing/clamping the cutters
-grinding the cutter so it will not rub against the wall
-editing tool number so it match the one in tool table
-editing coolant (changing from water to air/oil mist)
-changing rpm (on one machine we have only 10.000rpm)
-changing end of program (M30 to M5/M9).....

Some 30% of our programs are done outside and these guys do not have optimize post for our machines.

How to you handle these problems, how are you getting maximum efficiency out of your CNC centers?