The first seems compelling to me, less mass means less over all energy to freeze.
The second less so. Hot water has a bigger surface area, which makes heat loss fast at first. When it gets to cold water's temp it should have the same surface area as the cold water making the advantage disappear.
- 1 m³ of hot water is less water (in terms of mass) than 1 m³ of cold water
- 1 kg of hot water has a bigger surface area than 1 kg of cold water
I am still not convinced that this alone would explain such a phenomena. I'd rather believe there is some weird fluid dynamics and layering involved.