The reason is that with the eggs taking so long to hatch I put down to the egg shells being too thick.
The hatch method is :-
Yes, even temperature.
Yes, movement.
But the secret ingredient is the microworms.
They create an acidic environment which dissolves the egg shell.
That is why it is imperative that they are put into the bowl of water on your return, otherwise they will die from oxygen depletion.
I learnt that one day when | was distracted and I lost the whole tube.
You learn quickly with errors like that.
I hatched 100's of medaka eggs this way, ensuring that the babies were all the same age.
Oh!! Forgot to mention it, you get a work out that's healthy for you as well. Bonus.