The tension was already high between Jesus and the Pharisees. They turned their noses up at Jesus and ridiculed him (see Luke 16:14). Mockery is therefore contained in their question.
You talk much about the kingdom of God (see Mark 1:15), but is it really coming? Now let us see something of that.
Jesus answers by emphasizing that the kingdom of God is not coming in ways that can be seen.
The Greek word parateresis used here, comes from the world of medicine, and points to certain symptoms of an illness by which a diagnosis is made. But this is not how it works for the kingdom of God. That cannot be charted (like that) for us people.
20 Being asked by the Pharisees when the kingdom of God would come, he answered them, “The kingdom of God is not coming in ways that can be observed,