Proposition: Ice cream is kept in the freezer
Proposition: Ice cream is best if it removed from the freezer a while before consumption and allowed to warm and soften a little.
Proposition: Ice cream is desired NOW
Corollary: At any given time t the freezer has a compartment at the front which
contains ice cream which was removed from the freezer half an hour ago.
Explanation: The freezer is stocked with a number n of tubs of ice cream. They are mounted in a conveyor-type system. At specified intervals (say, 10 minutes) the conveyor advances one position. At any time, most of the tubs are in the deep freeze section of the freezer, and one of the tubs is in the front compartment at the perfect softness for consumption.
Proposition: The conveyor mechanism needs some kind of managed system to control the warming and softening of the ice-cream. I suggest a kind of paired heat exchange system whereby there are a series of paired compartments. So that as the conveyor advances, the tubs heading out to the front compartment are paired with the tubs heading back towards the deep freeze, in a way that there is a controlled temperature gradient and the heat for warming is captured from the cooling returns.
Corollary: The time lock is required to ensure that only the ready-to-eat tub in the front compartment can be accessed. There is no consumer access to any of the intermediate compartments. The deep freeze can be accessed to allow for re-loading with newly purchased tubs, and also to allow for emergency access to vast quantities of ice-cream should such access be necessary.