Not once in use. Insulin should be stored in the refrigerator until you start using a pen or vial. Once in use, a pen or vial can generally be kept at room temperature for up to 14 days (pens) or 28 days (vials). Because there are several different kinds of insulin, check your package insert for more information. Insulin should always be protected from freezing temperatures, or high temperatures (above 80-85f).
Until you open. The pen or vial and begin to use it. After that, keep it out of freezing cold, direct sunlight, or high heat. Most pens and vials will last for about a month if kept in a medicine cabinet or drawer in the bathroom -- then they should be discarded if some unused residual Insulin is still present.