I have only done it recently.... but didnt leave it long enough to be an icecream but it was kind of nearly an icecream they are so yummy! just cut the top off..
I would say a good few hours as I left mine for an hour and it wasnt long enough.. Enjoy..
I usually leave mine overnight, or longer. I cut the top off, put it in a bowl and then in the microwave for about 35 seconds so the outside starts to go a bit soft. The good thing is it takes a while to eat them too!