production order eff report

Dear experts,

I want make a production order effciency report. for that the formula is

efficiency = Actual exe.time / planned exe. time .

We get planned exe. time from AFKO table.

While calculating actual exec. time I have a problem.

I have 3 operations

10, 20, 30.

Operation 10 starts at 7 am, 20 at 8 am and 30 at 9 am.

From 9 am to 3 pm all three operations r under execution.

At 4 pm operation 10 completes, at 5 pm oper. 20 completes, at 6 pm oper. 30 completes.

Now I want to calculate the total exec time of an order, i.e. from 7 am to 6 pm but time betwen 9 am to 3 pm is to be considered only once as it overlapping time.

How to map this?

thanks

sanket