By the people for the people
Answer
Its 12 months
Explanation
According to IRS, it allows for a single tax-free rollover of a 529 account per beneficiary in a 12-month period. This 12 month rule should not be violated because it can result to a 10% penalty on the earnings. However, transfers across siblings are not considered rollovers.
I did some quick research, and your answer would be the Organisation for Economic Co-operation and Development. Hope this helps!<span>
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