The insulin vial/insulin pen, in use can be kept at room temperature i.e. at 24-25 degree centigrade till it finishes. The stock of insulin should be kept at 4-8 degree C, so that it is not spoilt. Insulin is a protein, it can get spoilt at higher temperature. You may use the same insulin for long time without any problem, all insulins of same type, of different companies are the same.