I am not an expert. I have done a lot of reading about parrots in general and cockatiels in particular. I have read 2/3 day in between eggs is normal.
My female grey has been laying eggs last month for a total of 5 eggs. the longest time between eggs was 5 days but averaged 3 days.
what you describe seems kind of a long time to me.
do you know if the eggs are fertile?
only thing I can think of is diet, if the bird does not have an adequate amount of calcium or some other vital nutrition it might take longer for the egg to develop.
Hopefully someone that knows more that I do has a better idea.
BTW on the subject of eggs does someone know what the symptoms of egg bind are ?
I would like to know what to be on the lookout for.
texsize