I think that when water is heated it expands . And we all are aware that ice has more volume than water . So as the cold water freezes it expands to turn into ice which takes time . As the hot water is already expanded it takes less time to form ice because the expansion of the hot water has occurred which makes it consume less time to form ice and expand . As soon as the hot water freezes If we check the temperature of the hot water ice it would be HIGHER than that of cold water which has not formed ice yet . Therefore hot water freezes faster than cold water because hot water is already expanded while the cold water needs time to expand . It is all about expansion of water . Well thats what i think and it is just my opinion about what i think . I may be wrong or i may be right .