That freezing efect and other reasons for it is fun theory. They all depend upon:
1. A comparison of water that has had the air boiled out to water with air still in it. Hot water pipes carry de-gassed water. Cold water pipe mains flow more water more often to fill basins and toilets, so tend toward less feezing.
2. The teenage student Mpemba sat the water on the porch to watch. the cups were sitting on frost, so the frost melted around the cup and gave better contact with the cold porch. Hope your pipes aren’t sitting in frost.
3. The third effect of convection doesn’t work well, because when the hot water actually gets to the same tmperature the cold started at, the convection rate becomes tha same as when the other water was cold.
But it is fun.