How to know when a commandBuffer starts rendering and when does it finish?

Hi guys.
I'm making a camera that renders all objects in the scene except objects with the tag "enemy".
The object can be excluded ( obj.SetActive(false) ) from rendering in the OnPreRender().
Then the object can be activated ( obj.SetActive(true) ) in the OnPostRender().
As a result, the camera does not render the object.

Now I'm using CommandBuffer and the "enemy" is rendered:
https://yadi.sk/i/CXOY7qvi3UdsFS
Here is the order of calling methods (https://docs.unity3d.com/Manual/ExecutionOrder.html ... just in case).
This is an example of how I add a buffer:
camera.AddCommandBuffer(CameraEvent.BeforeImageEffects, cmdBuff);

The problem is that I do not know how to set the command buffer so that it works after OnPreRender, but before OnPostRender. Is this possible?
How to know when a commandBuffer starts rendering and when does it finish?

 

Is the question quite simple or is it impossible to do it?