Answering Machine Detect(AMD), wait for silence?

I am using AMD, but my issue is there is too long of a delay in a lot of scenerios largely based on the example provided by

exten => s,1,NoCDR
exten => s,n,AMD
exten => s,n,GotoIf($[${AMDSTATUS}=HUMAN]?humn:mach)
exten => s,n(mach),WaitForSilence(2500)
exten => s,n,Playback(message-when-machine)
exten => s,n,Hangup
exten => s,n(humn),WaitForSilence(500)
exten => s,n,Playback(message-when-human)
exten => s,n,Hangup

Can I remove the WaitForSilence for Human, as I want my message to play immediately upon someone answering the phone, or is the WaitForSilence required for the AMD command to function properly?

I tried to test and it is not clear to me, as nothing I do is working 100%.

Not an expert but why the waitforsilence after detecting?