Millis() not working

[GolamMostafa]

@Declan

  timeBegin = millis();
  do {
    stepper17.runSpeedToPosition();
     toGoDistanceCounter++:
  } while (stepper17.distanceToGo() != 3520);
  timeEnd = millis();

@van_der_decken

that if you create a counter that counts the number of times your code executes that while loop,...'

  int toGoDistanceCounter = 0;

  timeBegin = millis();
  do 
  {
    stepper17.runSpeedToPosition();
    toGoDistanceCounter++:
  } 
  while (toGoDistanceCounter != 3520);
  timeEnd = millis();
  Serial.print(timeEnd - timeBegin); //should show non-zero value

The stepper17.runSpeedToPosition(); function must be executing for 3520 times for stepper to arrive at its final postion. So, you need a counter to count how many times the function has been exected as said in #3.