Education

To follow-up on the comments from @Hal_Al, there is no definitive guidance on the issue you raise.  There was some attempt to get clarity on the issue in 2008 when the Treasury Department issued the following proposed IRS Guidance:

"Section 529 is silent regarding whether distributions must be made from a section 529 account in the same tax year as QHEEs were paid or incurred. Concerns have been raised that individuals could allow the account to grow indefinitely on a tax-deferred basis before requesting reimbursement or use distributions in earlier years to pay QHEEs in later years. Accordingly, the IRS and the Treasury Department propose to adopt a rule that, in order for earnings to be excluded from income, any distribution from a section 529 account during a calendar year must be used to pay QHEEs during the same calendar year or by March 31 of the following year. The IRS and the Treasury Department welcome comments on rules necessary to ensure that distributions from section 529 accounts are appropriately matched to the payment of QHEEs."

However, the idea to add clarification to this situation never became a reality.  IRS Publication 970 which explains many matters of 529 tax law, makes no mention of reimbursement withdrawal deadlines.  Neither does IRS Topic No. 313, which explains Qualified Tuition Programs such as 529 plans. 

Consequently, some tax professionals recommend that the reimbursement for qualified expenses be effected in the same year that the expense occurred.  If this cannot be done, then perhaps reimbursing prior to March 31 of the next year may provide some back-up.  The point to remember is that there still remains no specific IRS guidance on the issue you have raised.

@soccerdad1