Novo Nordisk Pharmaceuticals Ltd – manufacturers of synthetic insulins, ‘human’ and analogues

This table with permitted temperature and exposure times applies to single exposures only and repeated exposures to higher temperatures will gradually reduce the efficacy of the insulin. It shows permitted temperature and exposure times that will not reduce the efficacy of the insulin, PROVIDED it is then returned to the refrigerator.”

Permitted Exposure Times For Various Temperature Ranges

• Insulin preparations should not be exposed to temperatures between:
• -20 to –10 degees C for more than 15 minutes
• -10 to –5 degrees C for more than 30 minutes
• -5 to +2 degrees C for more than 2 hours
• 8 to 15 degrees C for more than 96 hours
• 15 to 30 degrees C for more than 48 hours
• 30 to 40 degrees C for more than 6 hours
• Insulin should never be stored above 40 degrees C.
• It is important that insulin is never frozen, or exposed to a combination of high temperatures and excessive vibration.

source https://www.iddt.org/about/living-with-diabetes/storing-insulin