The findValue parameter for the X509Certificate2Collection.Find(X509FindType, object, bool) method must be a DateTime value in local time. For example, you can find all the certificates that will be valid until the end of the year by eliminating the results of a X509Certificate2Collection.Find(X509FindType, object, bool) operation for X509FindType.FindByTimeExpired of the last day of the year from the results of a X509Certificate2Collection.Find(X509FindType, object, bool) operation for DateTime.Now.