The judgment of God happens at each and every moment in accordance with the law of cause and effect. But the fruits of one's actions, the result of the judgment, can appear at any time. So at all times, be prepared for both God and the Devil. Heaven may call you, but if you are lethargic you may not hear its call! The Devil too, likes to pay a visit while you sleep.
It is not too difficult to extend control of the mind into the first bout of dreaming, but control is easily lost later in the night. The more you learn to cleanse your mind of deluded concepts during your waking life, the more easily you will be able to keep delusions at bay during sleep. It must become automatic: if there is effort, exhaustion follows.