Mesh pub/sub, max jitter on transmission delay?

Connectivity BLE // NFC
1

I have two devices, Argon / Xenon talking one way over mesh.
I am measuring the delay and jitter from transmission from Argon to reception callback on Xenon is executed.
On the transmitting end, the Argon, polls a button in loop() and does

if(meshConnected==1)
{
  digitalWrite(D7,1);
  Mesh.publish("shift","dn");
}

Reciever is just waiting for a telegram:

void setup()
{
  //Serial.begin(9600);
  Mesh.subscribe("shift", myHandler);
  pinMode(D7,OUTPUT);
}

void myHandler(const char *event, const char *data)
{
  if(ledOn)
    ledOn=0;
  else
    ledOn=1;
    
  digitalWrite(D7,ledOn);
}

I measure D7 on both devices, and observe a delay between 3[ms] to 7[ms], from one transmission to the next.
I assume the jitter of +/-2[ms] may be caused by the underlying scheduler, and background tasks.

Is SYSTEM_THREAD(ENABLED) the correct way to minimize jitter, and will it allow the Mesh.Publish to transmit deterministically.
How little transmission/reception timing jitter is possible with mesh/thread in the Particle implementation ?