I don't thunk your model is correct. Opening the fridge causes the accumulated cold air to fall out over a period of a few (maybe 4-7?) seconds, after which it doesn't really matter how long you leave it open, as the air is all room temp. The stuff will slowly take heat from the room temp air, at a rate of about 1 degree/minute. Once the door is closed, it takes a few minutes (again, IDK how long) to get the air back to 40F, and then however long to extract the heat from the stuff. If you are chosing between "stand there with it open" and "take something out, use it, amd put it back within a few minutes" there is no appreciable difference in the air temp inside the fridge for those two options - in both cases things will return to temp some minutes after the last closing. You can empirically test how long it takes to re-cool the air simply by getting a fridge thermometer and seeing how the temperature varies with different wait times. Or just see how long before the escaping air "feels cold" again.

The model here is not a very good one in one important respect: opening the door twice in quick succession does not cost anywhere near twice as much as opening it once.

When you leave open the door, the colder air falls out the bottom and drags more warm air in past the contents, raising their temperature quite rapidly. While there is some additional turbulent mixing in the airflow around the initially moving door, it is not really significant compared with the overall downward convection flow inside the fridge. The flowing air cools and falls out the bottom continuously.

When you close it again, the airflow quickly reduces to almost nothing as the air stratifies by temperature - the coldest air is no longer free to flow out. The rate of heat transfer into the food reduces substantially. Eventually the air cools via the refrigerated walls and starts cooling the contents back to an equilibrium temperature, though this takes quite a few minutes.

So in terms of the important thing - temperature of the contents - you're better off opening it each time as an open door heats the contents much faster than a closed one even with the same warm air in it.

The real answer is that you should minimize the risk that you walk away and leave the door open for hours, and open it zero times whenever possible. The relative heat loss from 1 vs many separate openings is not significantly different from each-other, but it is much more than 0, and the tail risk of "all the food gets warm and spoils" should dominate the decisions

Why are you asking? I'd say in general the answer is that you should be thinking about more important things. The consequences of getting the fridge timing either right or wrong are very small compared to many things in life. Social interactions and social skills are an overlooked area worthy of a ton of thought and analysis.