Function: mm:ss => int

        static int ConvertToInt(string timeStr)
        {
            int result = -1;
            if (!Regex.IsMatch(timeStr, @"^\d{1,2}:\d{1,2}$")) return result;
            string[] data = timeStr.Split(':');
            result = Convert.ToInt32(data[0]) * 60 + Convert.ToInt32(data[1]);
            return result;
        }