Matthew 17:18

‘And Jesus rebuked him, and the demon went out of him, and the boy was cured from that hour.'

Then Jesus rebuked the evil spirit and it came out of him. There was no spirit, whatever its power and importance, that could do anything but obey Jesus. He had bound their master, He had no problem, even as a human being, in controlling his minions. Matthew stresses the instantaneous nature of the healing. This might suggest that as one of the disciples he was very conscious of how long they had tried to do it and had failed.

For ‘from that hour' compare Matthew 8:13; Matthew 9:22; Matthew 15:28 referring to the centurion's servant, the woman with constant bleeding, and the Canaanite woman, in each case concerning people with insistent faith, and people who came to Him against the odds. He always responded promptly to determined faith.