If you read and understand the datasheet I linked you will see there are 2 parameters, integration_time and time_constant. The parameter time_constant is a static value set in the knock sensor parameters window, integration_time is configurable as a function of engine speed via the knock window settings.

 

I ask about this integrator time constant. Why 240?
How to choose this value?

 

Yes, and I pointed you to a resource that tells you what that value is and how it plays into the knock sensor reading as reported in MS.

Score: eggplant

think of that setting as a global gain, except smaller numbers give more gain, larger numbers give less. I believe this is also described in the MS manual, only they refer to it as a filter parameter.