I don't think that Pub 502 applies other than that medical expenses paid with funds from the HSA can't be claimed on Schedule A and to define the types of expenses that could be qualified medical expenses.
Section 223(f)(1) states:
Any amount paid or distributed out of a health savings account which is used exclusively to pay qualified medical expenses of any account beneficiary shall not be includible in gross income.
IRS guidance makes reference to medical expenses being "incurred," but doesn't seem to indicate whether or not the expense is incurred at the time it is paid or is incurred at the time the work is performed. I suspect that the repayment can be obtained from the HSA anytime after the expense is paid using other funds. Still, the longer that the funds remain in the HSA the longer the funds can grow via investments to be used tax-free for any qualified medical expenses that are incurred after the establishment of the HSA, so unless funds are tight, it would probably reasonable to wait to obtain the reimbursement.
