This link may help you - it's IRS discussion about casualty losses generally, and discusses the timeframes for a casualty loss to be deductible for tax purposes. Since the safe harbor definition references losses that would qualify for a deduction under section 165, it seems reasonable to look to whether or not it would still be deductible in assessing how-late-is-too-late:
http://www.irs.gov/taxtopics/tc515.html