using System;

public class Program

{

    public static void Main()

    {

        DateTime transactionDate = DateTime.UtcNow;

        string transaction_date = "20240815";

        string transaction_time = "011923";

        if (transaction_time.Length > 1 && short.Parse(transaction_time.Substring(0, 2)) < 12){

            var utcNow = DateTime.UtcNow;

            string amPm = utcNow.ToString("tt");

​

            //Method 1 - Safest way

            var timeOnly = DateTime.ParseExact(transaction_time, "HHmmss", System.Globalization.CultureInfo.InvariantCulture);

            var dt = DateTime.ParseExact(transaction_date, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);

​

            string newDateToString = string.Format("{0} {1}:{2}:{3} {4}", dt.ToString("d"), timeOnly.Hour.ToString().PadLeft(2, '0'), timeOnly.Minute.ToString().PadLeft(2, '0'), timeOnly.Second.ToString().PadLeft(2, '0'), amPm);

            Console.WriteLine(DateTime.Parse(newDateToString));

​

            //Method 2

            int hh = short.Parse(transaction_time.Substring(0, 2));

            int mm = short.Parse(transaction_time.Substring(2, 2));

            int ss = short.Parse(transaction_time.Substring(4, 2));

            string toString = string.Format("{0} {1}:{2}:{3} {4}", dt.ToString("d"), hh.ToString().PadLeft(2, '0'), mm.ToString().PadLeft(2, '0'), ss.ToString().PadLeft(2, '0'), amPm);

            transactionDate = DateTime.Parse(toString);

            Console.WriteLine(toString);

        }

        else

        {

            transactionDate = DateTime.ParseExact(transaction_date+transaction_time, "yyyyMMddHHmmss", System.Globalization.CultureInfo.InvariantCulture);

        }

        Console.WriteLine(transactionDate);

    }

}