You can "chance" it when he stays dry through the night consistently enough for your liking. For example, maybe you want him dry for a week... or maybe you don't mind changing sheets every 3 nights. I waited for Violet to be dry consistently - about a week. There were definitely times when it seemed she was consistent but as soon as I let her try without, she had an accident. I just told her that it simply meant that her body wasn't ready. Sometime before 5, she started to be able to consistently keep her bed dry. However, she does get up at night to use the toilet. I can't remember when she first started being dry... I think it was before 4 and a half, because I remember that when she had some medical issues that put her briefly back in diapers, we didn't have ANY diapers for her and had to buy some.
P.S. when I say "diapers," it was "pull-ups." Same thing in my mind except that pull ups are easier to put on an older child.