oh my god - that reminds me of a friggin hilarious family story from back before most of you were born. There is no way that ice lasts for 5 hours in the southeast - I give it an hour tops and in the mean time its blowing out p--- warm super humidified air on you.
The ice is concealed in a plastic container, so it wouldn't be spitting out humid air like a bucket full of ice would.
A frozen gallon of water will absolutely stay frozen for 4-5 hours. When I freeze bottles of water to go hiking, they'll last for hours and they're considerably smaller than a gallon.