I store mine in a shallow baking dish with a towel in it and turn them over a couple times a day. The eggs I have in the bator right now had all been in the fridge for over a week before I got a wild hair to incubate them. All 7 are developing well at 12 days in. These buggers are due to hatch Sat the 14th. I placed another one from the fridge a couple days after these and it's developing too. It's a white leghorn egg that I pulled randomly from the dozen Dad collects from his flock. I also may have put in 1 button quail egg to check for fertility and yep, you guessed it, it's growing too.
Everything I have read the coldest you can safely store chicken eggs is 50 F. I have been looking for a bit as I have a perfectly good dorm fridge empty, but here is the problem it allows the temp to reach 50 then kicks on the compressor and drops to 46. So I am afraid to put my girls eggs in it waiting for incubation.
Optimum temperature for holding hatching eggs is 55. Any hatching eggs held below 40 degrees will likely not hatch.
Hatchability percentages goes down over time, never up.
One problem with holding hatching eggs below 55 degrees is condensation forming on the shell. This could lead to the bloom being dissolved and the egg either suffocating or drying out too much.
During storage 60% humidity is not too much moisture as long as your eggs don't sweat.
After 10 days in storage hatchability starts to decline faster. At two weeks it really starts to fall. After 21 days you will be lucky to pip (not hatch mind you) one egg in two. That is if your eggs were stored in the most perfect conditions known to man. Setting twenty one day old hatching eggs is also when you see more birth defects arise in new chicks.
Hatching eggs should be moved but not turned three times per day
Failure to move hatching eggs while they are in storage will result in the embryos dying.