You are correct, that "normal time frames" for hay fires in barns are typically on the order of weeks to months. However, if you read the Ignition Handbook, on page 845 (first edition), there is a reference to post hay fires as a result of a flooding incident in Vermont in the early 1900s. The range was two (2) to three (3) days, with one incident taking four (4) days. This referenced document may provide some additional information that might be helpful in your investigation:

James, L. H., and Price, D.J., "Observations on Heating Hay in the Flooded Regions of Northern Vermont," Science, 67, 322 - 324 (23 Mar. 1928).

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
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