I'm probably alone on this....

If anyone fires the cannon only 4 times per day they will keep a surplus of elves up until some point in time between now and the end of the phase. I have calculated this out as the intended rate of fire based on the rate we get elves and the max amount we can fire in a set of 3. (144 + 12) / 39 = 4. This can't be coincidence that it is exactly divisible out to 4. At this point in time I have collected all elves possible daily and have been firing at about 5 times per day and my bank of elves has slowly dwindled once I was able to fire more than 10 per shot. Which means in a matter of days I will reach the point where I can only shoot it 4 times a day once I have 39 elves available to shoot. That should be as follows: Once when I wake up and once every about 5 hours. But if for some reason I can't shoot 4 times one day I will have those elves in bank for the next day and do an extra shot that day.