My DD8 was 3 years and 7 months before she no longer needed diapers at night. I know the exact time because we were on vacation and I had forgotten to pack diapers. I had tried to leave them off when she turned 3 but I had to change sheets about 3-5 times per week, sometimes more than twice per night. Couldn't deal with that... Since we were at someone else house, I woke DD up in the middle of the night to go potty. We made it without accidents but I was stressed. When we came back home, I left the diapers off but didn't wake her in the middle of the night anymore. DD had maybe 1 or 2 accidents per month. I didn't limit her drinking because it didn't make any difference with her, either. I don't remember when she stopped having accidents but it's been a long time.

I just got DD2.5 potty trained during the day and I have no intentions to leave her diaper off during the night any time soon. Luckily, we don't have the problem of her getting teased about it. I hope, she will be dry at night by age four. I don't think that there is a lot you can do to speed it up. I think, the problem is that needing to pee doesn't wake her up rather than her having had too much to drink...