I have a 3yo. Split from her dad last year. She spends two nights a week there and sleeps until 7-7:30 regularly, but at home it's 6-6:30. I honestly don't think he's making it up, and the only thing I can think at the moment is she's warmer there than here, it's just a warmer house.
So AIBU to set the heating to come on for half an hour at day 5am, in the hope it takes the edge off and makes her sleep longer??